Uninstall 8.0, install 8.1. These 2 versions are different, canĀ“t update to 8.1 xD
Or you can install 8.1 and switch pages to 8.1. You can use many versions at same time (7.4, 5.6...).
When need only 8.1, then after installing it and websites set(or will be only switch automatically to static version) to 8.1, you can uninstall 8.0.