1) Make sure all of the users processes are dead.
ps -u username
^will show you everything that user is running. Then to kill all of their processes:
ps -ef | grep admin | awk ‘{ print $2 }’ | xargs kill -9
(or you can su to them and run “kill -9 -1?)
2) Obviously as root, run the following:
usermod -u NEWUID username
3) Or, you could just edit passwd.
4) Either way, profit!
Helped from here.
