Личные данные изменились.

In Russian, данные is grammatically plural in this meaning. It literally means data/details/information items, so the verb must also be plural:

• Личные данные изменились. = Personal details have changed.

That is why the past-tense verb ends in -лись, the plural form.

Изменились is the past tense plural form of измениться.

It breaks down like this:

• измениться = to change
• past tense stem: изменил-
• plural ending: -и
• reflexive particle: -сь / -ся

So:

• masculine singular: изменился
• feminine singular: изменилась
• neuter singular: изменилось
• plural: изменились

Since данные is plural, Russian uses изменились.

The -ся / -сь makes the verb reflexive, but in many verbs it does not literally mean oneself. Here, измениться means to change or to become changed, while изменить usually means to change something.

Compare:

• Я изменил данные. = I changed the data.
  (someone changed something)
• Данные изменились. = The data changed / has changed.
  (the data underwent a change)

So the reflexive form is used because the subject is not actively changing something else; it is what changed.

Because личные данные is the subject of the sentence.

In Russian, the thing that performs the action or undergoes the change in this kind of sentence is normally in the nominative:

• Личные данные изменились.

Here, личные данные is the thing that changed, so it stays in nominative plural.

Adjectives in Russian must agree with the noun in:

• number
• gender
• case

Since данные is plural nominative, личные must also be plural nominative.

So:

• личный = singular masculine
• личная = singular feminine
• личное = singular neuter
• личные = plural

That is simple adjective-noun agreement.

Изменились comes from измениться, which is perfective.

That matters because perfective verbs usually present the change as a completed event or a result:

• Личные данные изменились. = The personal details have changed / changed.

If you wanted to talk about an ongoing process or repeated change, you would usually need the imperfective изменяться.

So in this sentence, the focus is on the fact that the details are now different.

Yes, very often you can.
Личные данные поменялись is natural and common in everyday Russian.

A rough difference:

• изменились = changed, became different; a bit more neutral or formal
• поменялись = changed; often sounds more conversational

In official contexts, especially on forms or websites, изменились is very common.

It can mean either, depending on context.

Russian does not have a separate grammatical form exactly like the English present perfect. The past tense here can be translated as:

• Personal details changed
• Personal details have changed

In many real situations, English would prefer have changed, especially if the current result matters.

Yes. Russian word order is flexible because case endings show grammatical roles.

The neutral order is:

• Личные данные изменились.

But you may also see:

• Изменились личные данные.

This can sound a little more focused on the event changed rather than on personal details as the topic. Both are grammatical.

Yes, личные данные usually means personal data, personal details, or personal information, depending on context.

It can refer to things like:

• name
• passport details
• address
• date of birth
• contact information

In legal or administrative contexts, личные данные is often best translated as personal data. In everyday situations, personal details may sound more natural in English.

Russian has no articles, so there is no separate word for the or a/an.

Also, Russian often omits possessives like my when the context already makes them clear. So:

• Личные данные изменились.

could mean:

• The personal details have changed.
• My personal details have changed.
• The personal data changed.

The exact English wording depends on context.

In the meaning data/details, it is normally used as a plural noun.

You will commonly see:

• персональные данные
• личные данные
• контактные данные

All of these are plural in Russian, and verbs/adjectives agree with them in the plural.

Not exactly.

• Личные данные изменились. = The personal details changed / have changed.
• Личные данные были изменены. = The personal details were changed.

The second version is a passive construction and suggests that someone changed them. The first simply states that they changed, without focusing on the agent.

So they are related, but not identical.