How to Uninstall and Reinstall Windows 7 Without Disc
Don't like Windows 10? As long as you've upgraded within the last month, you can uninstall Windows 10 and downgrade your PC back to its original Windows 7 or Windows 8.1 operating system. You can always upgrade to Windows 10 again later.
Even if it's been more than a month, you should be able to perform a clean install of the version of Windows that came with your PC using fresh installation media and its product key.
Go Back to Windows 7 or 8.1
If you've upgraded a PC to Windows 10—not performed a clean install, but an upgrade—you have an easy option that lets you revert to the last version of Windows. To access this, hit Windows+I to open the Settings app, click the "Update & security" icon, and then switch to the "Recovery" tab. You should see a "Go back to Windows 7" or "Go back to Windows 8.1" section. Click the "Get Started" button in that section to get rid of your Windows 10 install and restore your previous Windows install.
Windows will first ask you why you want to go back. Just pick anything, and then click the "Next" button.
Next, it will run you through a couple of screens where it asks if you want to try updating Windows 10 instead (to see if it makes anything better), and then reminds you that if you have a password, you'll need to remember it or disable it while you can. When you get to the final screen, click the "Go back to Windows 7 (or 8.1)" button to make it happen.
Windows will then restore your previous version, restarting your PC a couple of times along the way.
This Process Uses the Windows.old Folder
RELATED: How to Restore Your Files From the Windows.old Folder After Upgrading
Downgrading is possible because Windows 10 stores your old Windows installation in a folder named "C:\Windows.old" on your PC. You can see this folder in File Explorer, though you shouldn't attempt to delete it from here. You can also browse the Windows.old folder and restore files from it.
RELATED: 7 Ways To Free Up Hard Disk Space On Windows
Obviously, storing every single file from your old Windows installation takes a lot of space. If you open the Disk Cleanup application, you'll see just how much space it uses. Hit Start, type "Disk cleanup" into the search box, and then click the result to run it.
In the Disk Cleanup window, click the "Clean up system files" button.
In the list of files Disk Cleanup can remove, find the "Previous Windows installation(s)" entry, and can see just how much space it's consuming on your hard drive. If you're sure you don't want to go back to your previous version of Windows, use Disk Cleanup tool to remove those files and immediately free up space.
How to Downgrade if Windows 10 Doesn't Give You The Option
Assuming you have an old computer you upgraded to Windows 10, that computer previously had Windows 7 or 8.1 on it. That means that computer came with a product key that allows you to use Windows 7 or 8.1 on it. If you can't downgrade to your old version (maybe it's been to long, or maybe something went wrong with your downgrade attempt), you'll have to perform a clean install of Windows—something PC geeks often do on new computers, anyway.
RELATED: Where to Download Windows 10, 8.1, and 7 ISOs Legally
Thankfully, Microsoft now offers easy downloads for Windows 7 and 8.1 ISO files. Download the Windows installation media and burn the ISO file to a disc or copy it to a USB drive using Microsoft's Windows USB/DVD download tool. You can then boot from it and reinstall Windows 7 or 8.1 fresh, telling it to overwrite the Windows 10 system already on your hard drive. Be sure you have backup copies of all your important files from your Windows 10 PC first.
RELATED: How to Find Your PC's Windows Product Key So You Can Reinstall Windows
You'll have to find your PC's product key if you do this. On a Windows 7 PC, examine your PC for a "certificate of authenticity" sticker with a key on it. The sticker may be on the back of your desktop case, on the bottom (or inside the battery compartment) of your laptop, or it may have come on a separate card with your PC. On a Windows 8 PC, you may not have to do this at all—the key may be embedded in your computer's firmware. If so, Windows 8.1 will automatically detect it and allow you to reinstall Windows 8.1 without even asking you to enter a key.
If you bought a new PC that came with Windows 10 and you want to go back to a previous version of Windows, that's tougher. To do this legitimately, you'll need to purchase a Windows 7 or 8.1 license and install it from scratch, entering the product key you purchased during the install process.
If an important program or hardware device you use doesn't work on Windows 10, you'll want to downgrade. If Windows 10 just seems unstable, you'll want to go back to your previous version of Windows and wait a while longer before attempting an upgrade. Or, if you'd just rather hang onto Windows 7 for a while longer, you can downgrade. If you've upgraded a PC to Windows 10 once, you'll always be able to do it again later.
How to Uninstall and Reinstall Windows 7 Without Disc
Source: https://www.howtogeek.com/220723/how-to-uninstall-windows-10-and-downgrade-to-windows-7-or-8.1/