Hi, remove the action, it is held in with a few screws at the tops of the metal brackets. The screws usually have large knurled heads and are turned by hand after loosening with a screwdriver. The strings need to be cut out one at a time, after first taking off the tension with a tuning hammer with the appropriately-sized socket/head. There is something like 35k lbs. of string tension in an upright piano. Be careful, as strings can snap (explosively) while loosening.
Cut the strings out with wire cutters and dispose of one by one, or you'll have quite a tangle of strings. The cut ends will be very sharp, leather gloves and goggles are a must. The iron frame is very well secured to the wood frame with huge wood screws. Once the iron frame is loose, it can be broken to pieces with a sledgehammer for easier removal. Removing the keys and trapwork is fairly simple.
The best wood would be the heavy maple posts of the frame, and maybe the decorative work holding up the key cheeks. The rest is veneer over a substrate of inferior lumber. On better pianos, the case will have a lot of visible screws to remove, and still need some mallet blows to break the old hot glue joints. Inferior pianos may have early assembly screws veneered over so you may never find them. At any stage, you can wreck the veneer while breaking the glue's bond. Hot vinegar/water can be flowed into a joint to dissolve the glue, but too much exposure will also dissolve the veneer's glue, so it's risky both ways.
Be really careful with the string removal.
Casey