It is not possible to update a user id once it has been created.
If the user id was set up incorrectly or a user has changed names we have two options.
1. Leave the user id as it is and update the other info to the new info. You will want to remove the Approve security group, make the name change, and then add the security group back. Also, you will need to find any documents routed to the old name set up by searching route to, use my text, and enter the old name, then you can route those to the new name.
This is not recommended and can be very confusing
2. Delete the original user id and set the user back up with the correct info
Be sure to remove the user from all matrices before you delete the user.
See more info Delete User