I want to change my username or name in bitcointalk official account.but want to know that can i change that.please say me.
As others have said you have to donate 50
BTC to become a VIP which in turn allows you to change your username.
It's for the purpose of security & protecting the community. Somebody could become a scammer & then change their username & then return to scam somebody else etc.
The mods can't allow that to happen.