either use the itch app or install the new version at the same location as the old one. Your saves will still be there but you'll have the new version
after downloading the new version, extract it using 7-zip or any other archiving software. Look for the old version of the game and move the new version to that location. If a message pops up that there already is a file with that name click overwrite or something like that. If it does not pop up manually delete the old version. I do recommend to use the itch app tho since it makes updating a lot easier