Windows 7: Lenovo & w7 upgrade path?

I just bought this lenovo ThinkCentre M90 SFF (Refurbished) Lenovo Outlet - ThinkCentre M90 SFF Refurbished - Discounted Laptops, Cheap Laptops, Refurbished Laptops, Discounted Desktops, Cheap Desktops, Refurbished Desktops

It says it had originally had Windows 7 pro but the previous user had downgrdaded to XP pro. What is my best upgrade path to get Windows 7 back?

Anyone know if I got a good deal? Lenovo isn't selling this formfactor new anymore. Only SSFF & towers, and I can't find any reviews for M90's.
Dell has a deal for OptiPlex 380 Desktop PC right now for about $50 more, but the Dell small form factor can't hold two harddrives, while this Lenovo can. Plus to me the Lenovo looked to be the superior PC.

If it originally had Windows 7, there'd be a sticker on it with the Windows 7 edition and COA key on it. If you're able to read that, you just need to locate the Windows 7 installer (borrow or download), install that same edition then activate with that key.

The other option would be to call Lenovo and order recovery disks for this exact model. Normally these come cheap.