I bought the wrong product key (Windows 10 Home, without knowing this laptop has Pro installed!). I couldn't use it. I asked if I could get an exchange. They said they they could re-sell the product key if it was unused, which it was. I had to wait a couple of weeks and then email them back to ask if it had sold so that I could finally get the right product key. So It took a while to resolve but it is sorted out now. I guess, just be careful you're downloading the right product key because if you make a mistake it might take a couple of weeks to sort out. The system also said that I could ask for a refund (if I had gone ahead and bought the right product key straight away on top of the first one), but with a £1 fee. I'm glad it's all sorted out now but my experience was so-so.