How to rename user in JIRA ondemand?

[IgorP]

In user management i can amend user's fullname and email address, but not username.

[Joe Pitt]

that workaround won't change the username shown in the history. DO NOT delete the old username or you'll break the history display. You'll get a sql error if the username has been deleted. "Retire it' by removing it from all groups and roles that have access to any projects. I create a group named 'obsolete' and move them to that group so we know it is no longer an active user.

[Abdoulaye Kindy Diallo]

You can apply this workaround: https://confluence.atlassian.com/pages/viewpage.action?pageId=298979005