Hi
You can update to Windows 10 Technical Preview now, if you join the Insider Program, but you might want to consider waiting for 6 weeks and just update to the final retail version, you will save yourself some hassles with the multiple updates that will appear between then and now.
There are still some bugs in the preview versions.
Personally at this late date I'd wait.
If you don't like the Windows 8.1 interface you could install and use Classic Shell for the next 6 weeks instead of trying to get used to Windows 8.
You could use the Reserve Your Copy app, now, you should see an icon show up in the lower right of the screen at some point if it's not already there.
Mike