IMPORTANT: Make SURE rifle is NOT LOADED!
Your trigger guard has a small hole in it at
the rear (no jokes, please!)
Insert the blade of a small but sturdy flat head screwdriver into the hole. The shank and handle will be roughly parallel to the pistol grip at this point.
Now, pull the handle of the screwdriver towards the muzzle of the gun, away from the pistol grip. This will unlatch the hooks at the rear of the trigger guard.
If that doesn't work, do the following:
Get a long, sturdy rod or Phillips head (round shank) screwdriver. Place the screwdriver through the trigger guard at right angles to the rifle. Make sure the screwdriver is BEHIND the trigger.
Now, resting the butt of the rifle against your chest, and grasping the screwdriver with one hand on the handle and the other hand on the shank on the other side of the rifle, pull back (towards you) and away from the rifle.
NOTE: You may drop the rifle using this technique. Make sure that the rifle, if it slips and falls, lands on a soft surface so that it will not be damaged.
Once you do this a few times, it will seem very easy to do.