Dont know that much...
about Spyders, but if they are anything like Pirahnas then releasing the cocking hammer should be just a question of pulling the cocking rod back, holding it there, pulling the trigger and slowly releasing the bolt forwards.
The CO2: well there should be an on/off nob on the side of each of these bottles. Turn it off, dry fire the marker untill it is degassed, then unscrew.
Oh and first of all make sure you have no paintballs around
!
Sorry if this is not of any help, but I like to think I am helpful. Hopefully someone with more Spyder experience will post.
Remeber if its CO2 then its not THAT dangerous, just very cold! So wear gloves so that if it all decides to dump then you won't get cold burns.
Richard