As it was already said, if you want to change your ingame name and if you have an ingame account, you should contact a level 5 admin in any convenient way (ingame chat, IRC, forum PMs) and request it. If you don't have an account, you can just type a new name in your SAMP client.
If you wish to change your Forum name, go to Profile -> Account Settings, type a new name in the "name" input field and press a submit button on the bottom right of your screen.
Since your question is answered, the topic is going to be locked.
P.S.
Here you go [...]
