MySQL Server Administration with phpMyAdmin - Mastering phpMyAdmin 2.8 for Effective MySQL Management - page 257

For example, suppose that Bill calls and tells us that he prefers the login name billy
instead of bill . We just have to add a y to the user name, choose Local as the host,
and select delete the old one from the user tables :
After this operation, bill no longer exists in the mysql database, and all his
privileges, including the privileges on the bill database, will have been transferred
to the new user, billy. But bill is user definition will still exist in memory, so it is still
effective. If we had chosen the delete the old one from the user tables and reload
the privileges afterwards option instead, bill 's user definition would immediately
have ceased to be valid.
Alternatively, we could have created another user based on bill by making use of the
keep the old one choice. We can transfer the password to the new user by choosing
Do not change the password , or change it by entering a new password twice. The
revoke all active privileges option immediately terminates the effective current
privileges for this user if he or she is logged in.
Removing a User
This is done from the User overview section of the Privileges page. We select the
user to be removed, and then (in Removing selected users ) we can choose to Drop
any databases that have the same name as the users we are deleting. A click on Go
effectively removes the selected users.