Should I reset my iMac password?

Hello people

i hear different things about passwords being found out at the site of another company.

does it help to change your password after the facts?

and does it help to delete the account altogether in your passwordmanager?

and deleting it on the site of the third party?

I ask this because some people say that once the password is found out you cannot delete the combination with username that they stole.

I do not think that is true.

but will changing or deleting it in the passwordmanager be enough?

[Re-Titled by Moderator]