Windows 8.1 Preview

A trial version of the update for Windows 8 has become available for download.

To install, you need to download the update , restart the computer. When loading, the store opens, where it will be offered to update the system.
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There is a limitation: it works only where the system language is English.
Also, the blog advises to refrain from trying to make an update in the RT version with the installed language packs, because it's fraught. They promise to fix it soon.

There is no information about the need for a complete reinstallation, when the release version of the update (as with the test builds of Windows itself) is released, there are only a lot of questions on blogs.

UPD: In the comments they write that there is a link for the Russian version.