Я хочу поменять эту крупную купюру на мелкие монеты.

This is a very common Russian pattern:

• я хочу = I want
• поменять = to exchange / to change

So я хочу поменять... literally means I want to exchange...

Russian often uses:

• хотеть + infinitive = to want to do something

Examples:

• Я хочу есть. = I want to eat.
• Я хочу уйти. = I want to leave.
• Я хочу поменять деньги. = I want to exchange money.

This is about aspect, which is one of the biggest topics in Russian verbs.

• менять = imperfective
• поменять = perfective

Here, поменять is used because the speaker wants to talk about one complete action: exchanging one bill into coins.

So:

• Я хочу поменять эту купюру... = I want to exchange this bill...
  The focus is on getting the result.

By contrast, менять would sound more like:

• the general activity of exchanging
• a repeated action
• an ongoing process

For example:

• Я люблю менять валюту в этом банке. = I like exchanging currency at this bank.

Эту means this.

It is the feminine accusative singular form of этот.

Why feminine? Because it describes купюру, and купюра is a feminine noun.

Case matters too:

• купюра is the direct object of поменять
• so it goes into the accusative case
• feminine nouns ending in -а / -я usually change in the accusative singular

So:

• nominative: эта крупная купюра = this large bill
• accusative: эту крупную купюру

Because they form one noun phrase, and Russian makes the words agree in:

• gender
• number
• case

Here the phrase is эту крупную купюру = this large bill

Since купюра is:

• feminine
• singular
• accusative

the words describing it must match:

• эта → эту
• крупная → крупную
• купюра → купюру

This kind of agreement is extremely important in Russian.

Купюра means a banknote or bill, especially a note of a certain denomination.

Банкнота also means banknote and is very close in meaning.

In many situations, they are interchangeable, but купюра often feels especially natural when talking about:

• the value/denomination of the note
• changing a large bill into smaller money

So in this sentence, крупная купюра sounds very natural.

No, here крупная does not mean physically big. It means high-value or large-denomination.

So:

• крупная купюра = a bill worth a lot
• мелкие монеты = small coins / low-value coins

Russian often uses:

• крупный for something large in value, scale, or importance
• мелкий for something small in value, size, or amount

So this is similar to English a large bill, where large also means the amount, not the physical size.

After verbs like поменять in the sense of exchange X for Y, Russian often uses this pattern:

• поменять X на Y

So:

• поменять эту купюру на мелкие монеты = exchange this bill for small coins

Here:

• эту крупную купюру = the thing being given
• на мелкие монеты = what you want in return

This use of на is very common with exchanging one thing for another.

Example:

• Я поменял доллары на рубли. = I exchanged dollars for rubles.

Мелкие монеты is in the accusative plural.

The noun монеты is plural because we are talking about coins in general, not one coin.

Why does it look like the nominative plural? Because монеты is an inanimate noun, and for inanimate plural nouns, the accusative plural is the same as the nominative plural.

So:

• nominative plural: мелкие монеты
• accusative plural: мелкие монеты

The adjective мелкие agrees with монеты:

• plural
• accusative
• inanimate

Yes, very often you can.

Мелочь means small change.

So:

• Я хочу поменять эту крупную купюру на мелочь. would be a very natural sentence too.

Difference:

• мелкие монеты specifically means small coins
• мелочь means small change, which can sound more idiomatic and natural in everyday speech

If the idea is specifically coins, the original sentence is fine. If the idea is just change, мелочь may be even more common.

Yes. A very common verb here is разменять.

• разменять купюру = to break a bill / change a note into smaller money

So a very natural alternative is:

• Я хочу разменять эту крупную купюру.
• Я хочу разменять эту крупную купюру на мелочь.

That said, поменять is understandable and normal; разменять is just more specific to this exact situation.

The basic order is:

• Я = subject
• хочу = finite verb
• поменять = infinitive
• эту крупную купюру = object
• на мелкие монеты = exchange result

So the sentence is very neutral and natural.

Russian word order is flexible, though, and can change for emphasis. For example:

• Эту крупную купюру я хочу поменять на мелкие монеты.
  This emphasizes this large bill.

• На мелкие монеты я хочу поменять эту крупную купюру.
  This emphasizes what the speaker wants to receive.

But the original sentence is the most straightforward neutral version.

A helpful stress guide is:

• Я хочу́ поменя́ть э́ту кру́пную купю́ру на ме́лкие моне́ты.

A rough pronunciation guide:

• ya kha-CHOO pa-mye-NYAT' EH-too KROOP-nu-yu koo-PYOO-roo na MYEL-kee-ye ma-NYE-ty

A few notes:

• хочу́ has stress on the last syllable
• поменя́ть has stress on -нять
• э́ту has stress on the first syllable
• купю́ру has stress on ю
• моне́ты has stress on не

It can be used in both, and it sounds polite and normal.

In a bank, it sounds completely fine.

In a shop or café, many people might use something a bit shorter or more conversational, such as:

• Можно разменять эту купюру? = Can I change this bill?
• У вас можно разменять? = Can I get change here?
• Не могли бы вы разменять эту купюру? = Could you change this bill?

So your sentence is correct and understandable, but in real life Russian often becomes shorter and more direct in this situation.