It's pretty easy. After making sure it is unloaded, lay it on its right side (loading gate down). Remove the smaller screw in the left side plate and set it aside. That screw passes through the action and into the right side plate. Next, remove the large screw in front of the trigger that the lever pivots around. As soon as you have this screw out, the side plates will be free to fall off. Be careful, as the edges of the side plates are sharp!
As soon as you remove the side plates, you'll see the toggle links. There is one on each side. A pin passes through them and the lever. The pin rides in channels in the links. If you hold the rifle upright (in firing orientation) with the sideplates off and work the action, you'll see exactly how everything works. You'll need to reinsert the lever screw to hold the lever in place, of course, and with the side plates off the toggle links will fall out the sides if you don't hold it exactly upright, but it's kind of neat to see. When you move the lever down and forward, the levers fold. As one end of each link is attached to the bolt, that draws the bolt rearward.
With the links and pin out, you can remove the lever through the bottom of the action. You'll see that an arm extends from the lever pivot screw hole into the lifter. This is the lifter arm. It's loose now, because it was also held in place by the lever screw. You can remove the lifter arm by sliding it back into the space in the receiver vacated by the lever and links that you already took out. Set the lifter arm aside. Now draw the bolt all the way to the rear (cocking the hammer). The lifter can now be removed by just dropping it out the bottom of the frame. Voila, you're done. Just two screws removed, and the entire action is apart and ready for detail cleaning. Don't try to remove the bolt, by the way -- just leave it in place.
One other note -- you have have difficulty getting the lever screw out if the tension on the lever springs is too high. These are two small leaf springs inside the bottom of the receiver. They are adjusted by two very small screws that are visible on the bottom of the receiver right in front of the trigger. BE CAREFUL HERE. IT IS VERY COMMON TO BUGGER UP THESE SCREWS TRYING TO REMOVE OR ADJUST THEM! It seems that Uberti uses Bongo the 800 pound gorilla, armed with an impact wrench, to tighten these screws at the factory. You need to have good gunsmith screwdrivers that fit the slots perfectly. You should also soak them in a penetrating oil for some time if they don't want to loosen easily. If they don't come out easily, DON'T FORCE THEM! The metal is soft and they bugger up very easily. If that happens, you'll need to drill them out, so don't chance it. Another thing that works well for me is to secure the rifle upside in a vice (padded jaws, of course), insert the correct screwdriver into the screw slots, and give each a good sharp rap with a hammer. That often lets me break loose these screws.
Don't take the lever spring screws all the way out -- just back them out a few turns until the tension on the lever screw is low enough that you can pull it out. You can then also pivot the lever springs out to the side with the side plates off, making it easier to extract and reinsert the lever and lifter arm. Upon reassembly, the last thing you will do is gradually tighten each lever spring screw until you have just enough tension that the lifter drops when the lever is closed, and the lever stays closed.
Good luck, and good shooting! These are neat rifles. I love mine.
P.S. A little work with an Arkansas stone can make these the slickest lever rifles out there. Mine is a 44-40, and I can work it so fast that three pieces of brass are in the air at all times, while the sights stay on the target. I've had observers wonder if it was some sort of autoloader.
