If the lift kit installed on your vehicle and does not use new crossmembers then converting back to stock is as simple as removing the lift components and reinstalling the stock components. Things get more difficult when it comes to lift kits with new crossmembers. These lift kits most likely use a front differential drop and the factory frame had to be cut in order to make room for the front differential to be lowered down. In these instances the cut pieces would need to be welded back on if you wanted to return back to stock. Most people do not retain their stock section of frame which was removed, AND although possible, it would not be recommended to weld it in place for safety reasons. Please note the new crossmember kits only apply to IFS (independent Front Suspension) 4x4 trucks.
If you own a Leveled truck, you can return it to stock easily. This does not apply to “Level-Lifts” or any other kit which includes drop crossmembers. BUT! In many cases if you have a 6” lift installed, you can go down to a 4’ OR, upgrade to a different lift kit/ coilover conversion, OR go even larger! If you want some more information on removing a lift kit to install something else, check out this video.