easiest way to change steam account name?

your old profile names don't vanish when you change it though. they show in a little dropdown of previous names on your profile, so anyone can see what you used to be called. there's a clear previous aliases option in that same dropdown if that's the actual problem.

depends which one you mean, and this is where the question usually goes wrong. the name other people see is your profile name and you can change that as often as you like - edit profile, type over it, save. the account name you actually log in with can't be changed at all, ever. no setting for it, no support ticket. if that's the one bothering you then a new account is the only route.