First, remove the mag, pull the bolt back, and ensure the chamber is empty. Stick your finger in there to be sure you don't feel a case.
Next, push the lock lever back and let the upper & lower split apart- it is hinged. Grab the small metal rod (The bolt "Rat-Tail") and pull the bolt carrier/bolt out of the gun.
If you have a standard sheet metal top cover, it removes by sliding it backwards.
Next, use the tip of a bullet, a screwdriver, etc. to push in the retainer on the gas plug. Rotate it until the gas plug, gas piston & spring pop out of the gas tube. Pull the gas piston/spring out of the gas tube.
Viola, you are field stripped.