MySQL Server Administration - Mastering phpMyAdmin 3.1 for Effective MySQL Management - page 281

After this operation, bill no longer exists in the mysql database. Also, all his
privileges, including the privileges on the bill database, will have been transferred
to the new user— billy . But bill 's user definition will still exist in memory, and hence
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/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. Then (in Removing selected users ) we can choose Drop , to
remove any databases that have the same name as the users we are deleting. A click
on Go effectively removes the selected users.