Sponsored Links: Step 1. To find out which version your computer is running go to the Control Panel, then System and Security, and finally System. Along with other information about your PC or laptop, this will tell you precisely which version of Windows 7 it is. Windows 7 keys should work with either 32- or 64-bit versions of Windows 7, but you can’t swap Home Premium to, say, Windows 7 Ultimate. Step 2. To download Windows 7, head to Microsoft's websiteto download the correct version of Windows 7. Step 3. Now you have the software you can burn it to a DVD or - easier for most people - extract it to a USB flash drive. You can’t simply copy the ISO file you downloaded to a USB drive or DVD. Instead, you need a tool to do this, such as Microsoft’s own USB/DVD tool Step 4. Shut down your computer and insert your USB flash drive (or DVD). Now power on the PC and it should boot from the disc or drive. If not, you’ll need to enter the BIOS and change the boot order to prioritise the DVD drive or USB drive. Step 5. When you get your computer to boot from the disc or USB drive, you can install Windows 7. Be careful, though. If you’re planning to do a fresh install and format the hard drive as part of the process, make sure you’ve backed up all your documents, music, photos, videos and other files you don’t want to lose. Step 6. Once your irreplaceable files are safely backed up, you can follow the on-screen prompts to install Windows. If you're asked if you want to upgrade or do a fresh (clean) installation, choose the latter if possible. This will wipe your hard drive and is the best choice for most people as it doesn't carry across all the detritus from your old Windows installation. This improves performance and uses less disk space. NOTE: If your hard disk is split up into several 'partitions' you will need to either delete them all using the options available during installation, or choose one of the partitions on which to install Windows. You can delete or format (wipe clean) individual partitions, so if your data is all stored on the D: drive, say, and this is a separate partition on one physical hard drive, you can safely wipe the C: drive and install Windows on that partition without affecting your files. You will still have to reinstall all your apps and drivers, of course. As you can see, drive letters are not listed, so you'll have to go by the partition size. Just make sure you're certain before deleting or formattting anything.