I always take the right grip off first then carefully remove the left by carefully pushing up underneath while still having light pressure on the left grip with my left hand to maintain control of movement. Once I have some movement carefully work the grip out past the safety.
Reverse the steps to reassemble.
The operative words here are "carefully" with each step.
There is some more advice in this thread.
http://forum.lugerforum.com/showthread.php?t=22575