Note: By default, changing of username is disabled. You need to contact firstname.lastname@example.org to open momentarily.
Once it is enabled...
Please go to eAdmin > Members , click the " Book" icon of that staff
Then you can go to staff's profile and update the username and click " submit " button to save the changes
Please go to User Admin > then go to Staff profile by clicking the pencil icon on right most under Action column.
Finally amend the once done click