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#11
You have a legitimate licence for Windows 10 tied to this PC. You can wipe the disk (or replace it with a new one) at any time, then do a clean install of W10 and it will activate.
You don't need to uninstall anything. In Windows Setup you can choose do a clean install to an existing partition which will wipe anything that partition contains, or you can delete any/all existing partitions and install to an empty disk. See this tutorial...
Clean Install Windows 10
Yes, it is the same with Windows 7. In either Windows 10 or Windows 7, to do a clean install you boot from the USB flash drive or DVD containing Windows 7 or Windows 10. When you get to the option that asks if you want to do a Custom Install, select the Custom Install option. The next screen will show a list of drives and partitions. If you don't have a data partition that you want to keep (a separate partition that you only keep documents, photos, movies, etc on), then I suggest you just delete every partition listed until you get to one big unallocated space. This has effectively erased the hard drive. Then you select the unallocated space and click on next. Windows setup will set up the hard drive for Windows.
You can pick one of the partitions listed and click Next and Windows setup will erase just that partition and install Windows to it, but doing it that way can cause you to have a bunch of different partitions on your drive that you really don't need, like extra recovery partitions.
You can switch back and forth between the Windows 7 and Windows 10 on the same computer as many times as you want. Going back to Windows 7 will require a product key, but you can reuse the same Windows 7 product key on the same computer as many times as you want and switching to Windows 10 does not affect that. Once you have the first Windows 10 activated on that computer, you no longer need a product key for the same version of Windows 10 on the same computer. It will pick up the digital license saved for it from Microsoft.
There are certain types of Windows 7 OEM Product Keys that cannot be used to manually install Windows 7 with. If you check the product key with Showkey Plus from this forum and it says the product key is OEM:SLP, you cannot use that to manually to install Windows 7 with. That type of product key can only be used with factory provided recovery media. In that case you need to look for a Certificate of Authenticity sticker and use the product key printed on it. If Showkey Plus says the product key is OEM:COA - that key came from a COA sticker and can be used to re-install Windows 7 with.