Before I switched to a Corbin seat I had some difficulty removing the stock seat using the key so I looked for an alternate method to use in case the key stopped working completely.
If the key won't operate the lock mechanism a long screw driver can be used to operate the latch.
Insert the screw driver behind the left side cover by the top aft corner upwards at about a 45 degree angle pointing slightly forward. The idea is to gently push on the lever that is normally operated by the key. I practiced this with my old seat and it's pretty easy on a standard rocket.