Installation kits for Windows (and Linux) are built when a stable version is released (as described in http://www.tersus.com/#Id=1191).
Upgrades of an installed (stable) version to the latest version are always possible via the auto-update mechanism, as described there and in the Getting Updates page. Note that if your question arises from not being able to use the auto-update mechanism (due to network configuration issues), you can use the follow the instruction for Performing an offline manual update in the same page.
While we have no immediate plan to release a stable version, prior experience shows that one should not be far-off.
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