Change name

On my profile I put it before ny full name even its to long ,but one day I decided to change it for a short now ,and almost 2 days now im trying to put it back to my full name but I cant do it .what I must do ?

If your trying to change your user name you can't change it,only by deleting your account and make a shorter name OR have editor change it for you but you would have to give her a good enough reason to change it. Your display name can be changed when ever you want.