Awesome, thanks @joey1211 All done, my PC can finally breath again!
Thanks too to all the people who advised, it made it a very smooth process.
One tiny remaining issue. I've got an annoying 'System Reserved' drive letter showing up, which wasn't there before. I think windows usually hides that somehow, but the cloning made it visible as a drive. Is it an easy procedure to hide it again?

One tiny remaining issue. I've got an annoying 'System Reserved' drive letter showing up, which wasn't there before. I think windows usually hides that somehow, but the cloning made it visible as a drive. Is it an easy procedure to hide it again?