V případě, že se číslo účtu změní, pošlete nové bankovní spojení.

It means in the event that or in case that, and in this sentence it functions much like if.

So:

• V případě, že se číslo účtu změní... = If the account number changes...

However, v případě, že sounds a bit more formal and administrative than a simple když or jestli/pokud. It is very common in official instructions, contracts, and business communication.

Because v here is followed by the locative case.

The noun is:

• případ = case, instance

After v in the meaning in / in the case of, Czech uses the locative:

• v případě = in the case/event

This is a fixed and very common expression:

• v případě potřeby = in case of need
• v případě problému = in case of a problem
• v případě, že... = in the event that...

Because že se číslo účtu změní is a subordinate clause.

The structure is:

• main phrase: V případě
• subordinate clause introduced by že: že se číslo účtu změní
• main clause: pošlete nové bankovní spojení

Czech punctuation usually separates subordinate clauses with commas, so:

• V případě, že se číslo účtu změní, pošlete nové bankovní spojení.

This is very normal Czech punctuation.

Here se is part of the verb změnit se / změnit in the sense to change.

In this sentence:

• číslo účtu se změní = the account number changes / gets changed / becomes different

This is not the same as a fully reflexive English meaning like it changes itself. In Czech, many verbs commonly use se in ways that do not translate literally.

Compare:

• změnit něco = to change something
• změnit se = to change, to become changed

So:

• Firma změnila adresu. = The company changed the address.
• Adresa se změnila. = The address changed.

Because účet is in the genitive case after číslo.

Czech often uses this pattern:

• číslo + genitive = number of something

So:

• číslo účtu = account number
• literally: number of the account

Here:

• číslo = number
• účet = account
• účtu = genitive singular of účet

This is a very common structure:

• číslo domu = house number
• jméno firmy = company name
• konec filmu = end of the film

Because změní comes from the perfective verb změnit (se), while mění comes from the imperfective verb měnit (se).

In this sentence, Czech uses the perfective because it refers to a completed change:

• že se číslo účtu změní = if the account number changes / has changed into a new one

The idea is not an ongoing process, but a single completed result.

Very roughly:

• měnit se = to be changing, to change repeatedly or in process
• změnit se = to change completely, to become different

In instructions and conditions, Czech very often prefers the perfective when talking about a future completed event.

Formally, it looks like a present-tense form, but for a perfective verb it has future meaning.

So:

• změní se = will change

This is a key Czech pattern:

• imperfective present = present
• perfective present form = future

Examples:

• mění se = it is changing / it changes
• změní se = it will change

So in your sentence:

• že se číslo účtu změní = that the account number will change / if it changes

Here pošlete is the imperative, meaning send.

It can be:

• 2nd person plural imperative = you all send
• or formal singular imperative = please send when speaking politely to one person

In business or official Czech, this form is often used as a polite instruction:

• Pošlete nové bankovní spojení. = Please send the new bank details.

The verb is:

• poslat = to send

Imperative forms:

• pošli = send! (informal singular)
• pošlete = send! (plural or formal singular)

Because Czech usually omits subject pronouns when they are clear from the verb form.

The ending -te already shows that the sentence is addressing:

• more than one person, or
• one person formally

So Czech does not need vy here.

Compare:

• Pošlete to dnes. = Send it today.
• Vy to pošlete dnes. = You will send it today. / You send it today.
  This version sounds more marked, contrastive, or emphatic.

In normal instructions, the pronoun is usually left out.

In everyday English, you would usually translate it as bank details or bank account details, not literally bank connection.

In Czech administrative and business language, bankovní spojení commonly refers to the banking information needed for payments, for example:

• account number
• bank code
• sometimes IBAN/BIC, depending on context

So:

• pošlete nové bankovní spojení = send the new bank details

This is a set phrase in formal Czech.

It is accusative singular neuter, because it is the direct object of pošlete.

The noun:

• spojení is neuter

The adjective:

• nové agrees with it in gender, number, and case

So:

• nové bankovní spojení = new bank details / the new banking information

For many neuter nouns, the nominative and accusative singular look the same, so this form is not surprising.

Yes, absolutely.

That would also be correct and probably a bit more natural in less formal Czech.

Compare:

• V případě, že se číslo účtu změní... = more formal, bureaucratic, written
• Pokud se číslo účtu změní... = standard and natural
• Jestli se číslo účtu změní... = also possible, a bit more everyday
• Když se číslo účtu změní... = possible in some contexts, but can sound less precise for formal instructions

So the original sentence sounds like office, administrative, or legal Czech.

Yes. Czech word order is flexible, although different orders can sound more or less natural depending on style and emphasis.

The original:

• V případě, že se číslo účtu změní, pošlete nové bankovní spojení.

You could also say:

• Pošlete nové bankovní spojení v případě, že se číslo účtu změní.

Both are grammatical. The original version puts the condition first, which is very common in instructions.

In formal writing, putting the condition first often sounds clearer:

• first the circumstance
• then the required action

It is grammatically an imperative, so it is technically a command form, but in real use it sounds more like a formal instruction or polite request.

In business or administrative Czech, imperatives are often used in a neutral instructional way:

• Vyplňte formulář. = Fill out the form.
• Zašlete kopii dokladu. = Send a copy of the document.
• Pošlete nové bankovní spojení. = Send the new bank details.

So it is not rude by default; it is standard official style.

Yes, zašlete would also work, and it may even sound slightly more formal.

Compare:

• pošlete = send
• zašlete = send, dispatch, submit

In official correspondence, zašlete is very common:

• V případě změny zašlete nové údaje.

So:

• pošlete nové bankovní spojení = completely fine
• zašlete nové bankovní spojení = also fine, perhaps a bit more formal or written

Yes, in this sentence it is singular:

• číslo účtu = the account number / number of the account

That suggests one account number is being discussed.

If you wanted plural, you would need a different form, for example:

• čísla účtů = account numbers

So the sentence is talking about a single account number changing and asking for updated bank details.