Dude you should be able to go from 8 to 8.1 for free, then once that is done upgrade to 10 for free
Check you laptop manufactures website as they usually have a free upgrade path to Windows 10. With Windows 10 once you upgrade, you will not need a key as it will utilize your hardware for verification if you want to do a clean install later on.
You will not need to change your hard drive as the win 8 key is usually stored in the bios on 2012 and present laptops.
If I were you I would see if Xaeno or one of the GATT staff would assist you with the upgrade process as they offer a Tech service for a fee.
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