Delete alias and use it as new username

Greetings!

I would like to use my alias as my username.

(1) I deleted the alias from the alias field, logged out, and logged back in.
(2) The alias field was blank.
(3) I tried to change my username to my (former) alias, and received a message saying that the alias was invalid to use as my username. So it seems that deleting the alias in the alias field didn't delete it?

Can you delete the alias for me so that I can use it as my username? The alias was/is AlanNavarre@riseup.net

Or is there something else that I need to do?

Thank you very very much!
Alan Navarre