Make sure all of the parts are included. You should have:
1 x magazine catch
1x magazine catch lever
1x 6-32 flat head screw
Make sure your rifle is unloaded/empty and safe.
Remove the action from the stock by removing the two action screws, one in front of the trigger guard, and one in front of the magazine well.
Remove the rear action block from the stock by pressing it up from the bottom. It is simply held in by friction.
Remove the pin holding the magazine catch in place. Be careful not to lose any parts, the magazine catch is under spring pressure. This pin also holds the ejector in place.
Using the original pin, install the new magazine catch in the place of the original. Note the cutout on the side for the ejector.
Replace the rear action block in the stock. Press it down firmly until it is seated in place.
Install the magazine catch lever using the supplied flat head screw. A small dab of light duty thread locker is recommended but not required. Do not exceed 7 in-lbs!
Install the action back into the stock, using the manufacturers instructions.
Perform a function check to make sure your rifle is safe and ready to fire.
