I'll give it a shot - if someone knows a better way, feel free to correct me
To uninstall then reinstall a game from your Steam library:
- Unless you want to re-download the game, you'll need to make a backup of the game that is already installed on your PC. Note: this will not backup any skins or mods you have installed for that game (like the TF2 32-player hud or the awesome scout rainbow bat skin)
- To make a Back-Up of your game: go to the My Games tab in Steam. Find the game you want to backup, alt-click on it, and select Backup game files.
- A window will appear with your game listed. Select next, and choose where you want the backup to be stored on your PC. (the default is c
rogram filessteamBackups). If you're happy with this location, select next.
- Now you can select the file size for the backup. The default is CD (640MB). If you would like to burn the backup to removable media (CD, DVD) select the appropriate size. Note: You DO NOT have to burn the backup file to a CD or DVD for it to work. You can run the backup from your hard-drive or copy it to a flash drive and it will work fine. You can also select custom, input a larger file size (like 10000 MB) and it will create one large file. If you do not plan to burn a DVD to store the backup, this would be your best option.
- After you complete your backup, you can delete the game from your harddrive. Go to the My Games tab in steam, alt-click the game you want to remove, and select Delete Local Content.
- Once the game has been removed, you can now open the backup folder you created previously (c
rogram filessteamBackups). There will be a few things in this folder; you will need to click on the Restore Backup program file.
- Follow the directions to re-install your game.
Hope this helps!