It all depends on what your goal is. It is not difficult if you want to demo the existing cabinets and countertop to replace them entirely. It simply requires a sledgehammer, a drill or screwdriver, and a saw to cut the pieces into manageable sizes. It is more complicated if the goal is to remove cabinets but keep the existing countertop in place. You’ll have to prop up the countertop with 2x4s or other supports while removing the existing cabinets. You’ll also have to work around the plumbing, making sure not to damage any of it. (Make sure you first undo the screws connecting the cabinets to the walls.) Once removed, ensure you scrape off any glue residue on the bottom of the countertops before installing the new cabinets.