Glock doesn't make an extended slide stop for the G36. The ones you'll find from various retailers are modified versions of the extended slide stop for 9/40 models. Some have reported that they work fine, others that they don't work properly.
For the slide stop, you'll need a 3/32 inch punch like the Glock Armorer's Tool. You push the locking block pin(top pin above trigger) out first, then wiggle the slide stop forward and rearward and up and down while you push out the trigger pin(bottom pin above trigger). Once you have the two pins and the slide stop out of the frame, you reinstall the locking block pin. Then you insert the slide stop into the frame, and insert the trigger pin, again you may have to wiggle the slide stop around to get the trigger pin in.
You must install the locking block pin BEFORE you install the slide stop and trigger pin. Doing this ensures that the slide stop spring goes to its correct position under the locking block pin to give the spring its tension. If you do it in the wrong order, the slide stop spring will be in the wrong position and may be damaged, and you may see the slide lock back with rounds still in the magazine.
Here are some detail strip resources if you need them:
[ame]http://www.youtube.com/watch?v=oV0wDDFV0NY[/ame]
On the following page are some Glock Armorer's Manuals, just scroll down to the "G" section. I learned from the Update Manual and 2009 Manual. The 2009 Manual has a few pages missing, but that info can be found in the Update Manual as well.
http://stevespages.com/page7b.htm