I just received an email that someone was trying to change my password on Revolut community. to avoid this problem I immediately change my password.
I also want to change my username but I do not know where, because is not possible on my profile. Help me please.
Unfortunately it is not possible to change your username on Discourse forums (Discourse is the forum platform used here.).
As long as you have a complex password, it should be fine. Ensure that you use a unique password for every single website (This can be made easier by using password managers like 1Password or Lastpass).