Let's say Nick Gammon wanted to change his nick name to Chooks.
Many forum programs use the user name as the main index, it is not therefore something that is designed to be changed without some hands-on SQL coding. I don't know if that it the case here or not.
You really cannot change your login email, it will be reset on the next login. To use another email you need to create a new account. For us IDs are emails (at least now, could change in the future).Thanks,Luca