The game downloads on the Download Promotion Wars page will always be the latest version, including the latest fix and all the fixes before it.
If you already have Promotion Wars: 21st Anniversary Edition installed and want to update it to the latest fix, choose the Basic Download. This will unzip a folder containing the latest version of the game, including all fixes. You can then delete your old game folder, but remember to move across anything you want to keep such as your Saved Games, or any Data Packs you may have added yourself.
You can simply move the whole Saved Games folder from your previous version, into the main folder of the new version, to replace the one already there.
You can simply move the Data Packs you want to keep, from your old Data Packs folder, into the Data Packs folder of your new update.