With the barrels off.
If it has a hard buttplate, remove one screw and loosen the other. If it has a rubber recoil pad, look for two screw holes. They could be small round holes on some factory pads or could be nearly invisible cuts in the rubber that close up. For a rubber pad removal, try a #2 phillips screwdriver with some vaseline or handlotion on the screwdriver. It may be a slot screw, but more likely a phillips. Same removal as the buttplate, remove one screw and loosen the other, swing aside.
Look down in the hole and see what kind of bolt head you see. It could be a large slotted head or allen type head or hex bolt. loosen it a couple turns and give the driver tool a rap with the palm of your hand. You should see the receiver move forward a hair. Loosen another couple turns and rap it again. Remove the bolt, pull the receiver from the stock
