This is for the standard safety and not the J-lock. If it's a J-lock you'll need a replacement detent ball and spring.
Remove the trigger assembly. Directly above the safety you will see a small (about 3/32") pin running horizontally. This pin retains the detent ball and spring for the safety. Use a punch to push this pin out. You will see the vertical hole for them above the pin. Hold your finger over the hole or you may be looking for the spring.
Once the pin is out, remove the spring and detent ball. The safety should now be able to be removed. Insert the extended safety, replace the detent ball and spring and reinsert the pin.