Pro License users are able to specify in their License Manager that they can get test versions of eM Client. Otherwise, unless Support gives you a link to an 8.1 internal build, there is no way to get it.
I am sure that the official release will not be that far away though. Just keep an eye on the Release History.
8.1 has been released today. Sorry, I did not see that. You can now download it from the Release History.
There is nothing extra you need to do as either a Free or Pro License user, though it may be an idea to make a backup before. Otherwise just download and install, and your license will be there as normal.
Updates are not available to all users at the same time. It may be that it will only show there tomorrow or later. But you can always check in the Release History and download it manually.