You can do either. Personally, I never reinstall and try to keep files. Windows develops issues over time as it is. To do that is just asking for a shorter time before a reinstall is necessary. Just my opinion.
I don't know whether an upgrade install will retain optimizations. I doubt it.
If you do a clean install, make sure you either create a new partition over or format the existing Windows partition/drive, because otherwise the install process will retain certain files, even from 32-bit Windows.
Good luck
![Wink :wink:](./images/smilies/icon_wink.gif)