how many times to change themeforest username ,
I don’t know if Envato restricts username changing, but if you changed your username once and you want to change it again, you need to contact support team.
Cheers!
I believe the limit is once per annum, but if you require to change it more like @OsamaSayegh stated please contact the Envato support team 
I change my usename first time nothing change before
3 time in a year