My PC, bought 'refurbished' with Windows 7, updated itself to Windows 10 when the offer to do so came up. I've never had a more stable Windows since (although XP was pretty good from that point of view...). If, then, the PC is up to it (motherboard support for 64-bit..?), I'd recommend Windows 10 Pro, 64-bit. Mine is an HP8200, i5 processor, 12 Gb RAM
Hops this helps.