Hi,
After you have uninstalled Silent Hunter III you need to delete the SilentHunterIII folder from the drive you installed to, it will be in a folder called Ubisoft - don't delete the Ubisoft folder if you have other games by them installed. Also, you need to delete any SH3 related folders from My Documents then you can do a clean install of Silent Hunter III and patch to 1.4b.
Sincerely,