On yahoo messenger, how do i change my username? Ex: it's shows Ariel 2 all my friends & i want it 2 say Liera

On yahoo messenger, i type messages to people. when we chat, it'll say their username and then it'll say mine. Mine says Ariel and they can see that. I want it to say Liera instead. so everytime i write to them, it would say Liera instead of Ariel. How do i change that?