"not supported" =~ "It might work, but we aren't obligated to help you make it work" Others have posted that the old versions of Sage 50 works on Windows Vista, and 7. I installed the 2007 release and it worked fine (and the fonts on invoice screens were big enough to be readable!).

But... you're on your own if it doesn't work / stops working, and everyone needs their accounting system to be reliable.

As for the upgrade procedure, if I were to buy an update from Sage directly, I would make it clear to whoever you talk to that converting your 2006 data has to be part of the deal. As in 'full refund' if they can't help you get it converted.
 
Sage made a decision to stop supplying the conversion with recent releases. It's quite probable that some of the conversions (say, 2006 to 2007 or 2007-2008) would not run under Windows 10, so they had to take them out.

So you will need to first download an older release to your Windows 7 workstation to convert it up to a point, then install the one you bought to do the final conversion from that point to the current release.

A Sage Partner should be able to help you as well, but Sage doesn't pay them to help you and they can't work for free.