User Activity

Would like to change my user name, can't find how to do it.
I'd like to change my setting to private but don't know how, need help 
From now on I'll be leaving positive feedbacks for all deserving sellers. if I have any trouble with a seller I just won't leave any feed back, that way I won't be harassed. A selling is coursing me so much grief I feel sick. I'm ignoring him, been t...
I'm waiting on a few thing to arrive, and money's back once I have all that sorted, how do I go about closing my account?
I left a negative feed back to a seller who admitted he never posted item after telling me many times item posted, I left feed back saying that item was never posted, well now I won't to change my feed back ( reason being he is ring me sending messag...