If you say that you want to keep the saves when you uninstall, and then you reinstall the game, it should still have the saves and you shouldn't need to do anything.
That's assuming that you installed it to the same folder both times and on the same Windows account. If you installed it to a different spot, copy all of the files from the old location to the new one but don't overwrite anything. If you used a different account last time, you should be able to just log in as the other one and play it. Whether these would matter or not depends on how the game is set up; it can either store save data in the user account folder or as part of the game data.
So, make sure you're able to load your saves now. If not, make sure you're logged in as the user you were last time and installed the game to the same directory.