It seems pretty likely that your copy of Poser 8 is bogus and you may very well not be able to upgrade from it - but you could try.

There doesn't seem to be any discount for upgrading from Poser 5. Personally I believe it is worth skipping Poser Pro 2010 and going straight to the Poser 9/Pro 2012 level, because the differences are huge. The difference between Poser 8 and Poser Pro 2010 is mostly related to Gamma Correction, and Bagginsbill's shaders do a very good job of Gamma Correction in the non-Pro versions of Poser.

The current generation of Poser is faster, more powerful and totally worth the money. To take advantage of your 64 bit system you should get Pro 2012. Otherwise wait and save up for it. Or investigate the feasibility of buying a legal copy of Poser Debut and upgrading from that.

Poser 11 Pro, Windows 10

Auxiliary Apps: Blender 2.79, Vue Complete 2016, Genetica 4 Pro, Gliftex 11 Pro, CorelDraw Suite X6, Comic Life 2, Project Dogwaffle Howler 8, Stitch Witch