Here is a well illustrated article on straightening a leaning garage with a come-along (winch). I’ve used this technique on a garage with a much greater lean than this one with success. Other mounting methods such as a U-bolt and mounting the winch on the inside of the garage may be easier: ‘…a parallelogram can be forced back into a rectangle, if one diagonal (the longest diagonal) is pulled together. Also, the shorter diagonal could be pushed apart. Which method is chosen depends on the tools at hand. I happened to own a pair of 2 Ton cable winches (also called a “come-along”) as well as 6 Ton and 12 Ton hydraulic bottle jacks. I chose the weakest of my tools for the first attempt…’ Do this at your own risk, but it worked well for me.