It will be read automatically on reinstall if your computer is from a manufacturer such as Dell or HP etc. Windows 8.1 or 10 users will either have a separate key if Windows was purchased as a standalone product or the key will be embedded in the system BIOS. Windows 7 users will have a product key sticker.

You need a legal Windows license or the new install will be in trial mode.

For example, you can replace Windows 10 Home 32-bit with Windows 10 Home 64-bit.

You can switch between 32-bit and 64-bit as long as the Windows edition is the same.

If you have Windows 7 Home Premium, you must install Home Premium again.

Your Windows license only allows you to reinstall the edition of Windows that you have a license for.

Things to know about Windows ISO images and Reinstalling

Here we show you several ways to download the Windows ISO you need so your operating system can be installed cleanly and safely.

Microsoft prefers consumers to download a Windows 10 ISO from the Media Creation Tool instead of a direct download. It used to be easy to download Windows 7 ISO images until they were all removed from Digital River after sales of Windows 7 were discontinued in 2014. The best way to guarantee you are getting a clean and untouched Windows ISO image is by going directly to Microsoft themselves. Using a trusted source for the download is the preferable option. Of course, there are many unofficial sources but the files have often been cracked, tampered with or altered in some way. However, it’s more difficult to source official install media for older operating systems like Windows 7. It’s easy to get hold of a Windows 10 ISO image, burn it to DVD or write to USB and do a clean install. It’s also a good idea to clean install Windows 10 after upgrading so you are not transferring problems from your old Windows install. Simply using Windows over time will eventually degrade its performance. It doesn’t really matter what version of Windows you have, the best way to get your system working at its full speed and as issue free as possible is with a clean install of the operating system.

Windows 7 ultimate sp2