How can I change my Apple ID?

If you want to do a name change on your Apple ID, note the restrictions in the article.

Apple ID Name Change.        

 What to do after you change your Apple ID or password - Apple Support    I suggest doing this before you change your Apple ID or password.

Did you mean to mark your own reply as the solution?

Do you want to change which of two existing Apple IDs your iPad is using, or do you want to have the same Apple ID change its name?