I bought a pc at overclockers.co.uk and it came with windows 8.1 OEM not the retail version, my question is can you upgrade to windows 8.1 pro the retail version if you have windows 8.1 OEM on first
You should be able to do an "anytime upgrade" for the cost difference. (Now in the Add Windows Features menu) This will replace your old key, and be a perpetual one machine at a time key.