Put on eye protection to be sure you don't get struck in the eye with a flying part.
Unload the gun, and take all the ammo out of the room.
Take out the magazine. Pull back the slide.
Make sure it's unloaded.
Make sure it's unloaded again.
Make sure it's unloaded a third time.
Point it in a safe direction. At something that you don't care about putting a hole in. Something that's big enough to stop a .22 bullet. Not anything alive, or that has something alive behind it.
Pull the trigger.
Push in the moving piece at the back of the slide. (This is the piece that has a hole in it through which the back of the firing pin protrudes.) It retains the firing pin and the firing pin spring, so there's a bit of tension to it.
Lift up the back of the slide. The recoil spring will move the front of the slide forward. Allow the front of the slide to come off the front of the barrel. Remove the recoil spring to the front.
Carefully allow the firing pin retention piece in the back to back out of the slide. Tip the slide so that the firing pin and firing pin spring fall out into your hand.
That's as far as field-stripping is intended to go on the J-22. Reassembly is in reverse order.