The extended magazine release replaces the stock button release. Instead of pushing up on a button you now have a lever to push. Hope that makes sense. Here is a link,
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=670736Standard disclaimer applies, it was the first site i noticed with one.
There are also different shapes for the lever, so do a little research. You might want to shoot it for a while and then start modifying your rifle. Everything on a 10-22 can be changed, so if you don't like the function of something there is a modified part out there.
For mine i changed the stock. The barrel, 22" tapered s/s, don't like the look of the bull barrels that are popular with the target crowd. Mine will shoot five shot strings inside of your thumb nail at 50 yards with wally world ammo. Also added the extended mag release, the easy to use bolt release, and a new drop in trigger kit. The trigger kit reduces the trigger pull to 2 lbs. So don't ask me how much my $80 pawn shop rifle really cost me.