he has changed or he changed?

[turkyash]

Hi, I am trying to learn the English language and the verb tense is giving me a difficult time.

Which is correct?

He has changed his password.

He changed his password.

Any explanation would be appreciated.

Thanks

[English Freak]

Hi turkyash,

Welcome to this forum.
Your first sentence is in present perfect. (structure: have / has + past participle) while the second one is in simple past. Both of them are correct and make sense. It would be difficult to go for one of them when there's no context.
But keep in mind that:
We normally use present perfect to talk about something that happened at an unknown time in the past. So we can never use present perfect with a particular time expression (e.g. yesterday, two hours ago, etc.)
And we use simple past to say that an action happened in the past and it's finished.

[turkyash]

Thank you so much for answering.

I have another pair of sentence

If I had punched him then I would lose this case.

If I have punched him then I would lose this case.

Which one is correct|?

[5jj]

If I had punched him then I would lose this case.

Only the first is possible. The past perfect in the if-clause tells us we are dealing with a counterfactual past situation - I did not punch him.