In some ways, it was generous of Microsoft to offer the option in the first place. We've already explained step-by-step how to use the Windows 10 rollback feature.
But after a month, the option will disappear along with your old version of Windows, and you're then stuck with Windows 10. It's not such a hardship - see our Windows 10 review for why - but if you're only just discovering incompatibilities, what can you do about going back to Windows 7 or 8?
Here are some options open to you.
How to downgrade Windows 10 after 30 days: a clean install
Once 30 days have elapsed since you upgraded to Windows 10, it will automatically delete your old Windows files (kept in a folder called Windows.old) along with the files in two other important hidden folders: $Windows.~BT and $Windows.~WS.
You can check for these folders by enabling 'Hidden items' in the View tab in File Explorer. But even if those folders are present after 30 days, it's likely the files within them have been removed to prevent them using up a lot of unnecessary disk space. This means you can't roll back.
One obvious way to get around this is to use your Windows 7 (or 8) disc and activation key. It's not exactly a simple process since you'll need to back up everything and then wipe your hard disk and start from scratch. After installing Windows, you'd need to install drivers for your hardware, then all your software, and finally your documents and all the other files and settings you backed up. And, of course, hundreds of Windows updates.
If you have a disc but lost your activation key, you can extract it from Windows 10 by pressing the Windows key and R to bring up the Run box. Then type cmd and press enter. Then copy and paste this code at the command prompt which will have popped up:
wmic path softwarelicensingservice get OA3xOriginalProductKey
Hit Enter and your original product key for the previous version of Windows will be displayed.
How to downgrade Windows 10 after 30 days: Factory restore
Many laptops and PCs have a hidden partition on the hard drive which contains a copy of the original Windows, programs, drivers and settings which were on your PC when it arrived. Upgrading to Windows 10 shouldn't have affected this, so it should still be intact.
Whether or not you can access it is another matter. Typically you can look out for a message while your computer is starting up, such as "Press F11 for recovery options". When you press the appropriate key, you should be presented with a menu that will include the option to restore factory settings. For more details, including which keys to press on different laptops, see How to reset a laptop to factory settings (this applies to some PCs as well).
On some computers, you'll still have a Windows application which allows you to perform a restore by using the manufacturer's own method. On an Acer Aspire laptop, for example, we found the Acer Recovery Management app which made it simple to go back to the original version of Windows which came in the box.
Performing a restore will wipe the C: drive, so you will lose all your personal files and settings. So you'll still have to back these up, and you'll still have plenty of Windows updates and programs to install after the restore is complete. You shouldn't have to worry about anything not working, since the drivers will be reinstalled. But any hardware you've added will have to have the software or drivers reinstalled, such as a printer.
How to downgrade Windows 10 after 30 days: Third-party backup software
If you're thinking of upgrading to Windows 10 (or have just done so) and don't want the 30-day limit, there are two different options.
Hard drive imaging software is nothing new: Acronis, Norton Ghost and similar programs have allowed you to make a complete copy of your hard disk so you can quickly go back in the event of a hard drive failure, or some other disaster. You can use these, or something specific such as EaseUs System GoBack which is designed to let you roll back to a previous version of Windows.
Naturally, you need to install and use this type of software BEFORE you upgrade.
If you have already upgraded but are within the 30-day rollback window, you can enable hidden items (as described above) and rename the three folders which Windows will try to delete. If it can't find the folders - because you've changed their names - it can't delete them. We can't verify this works, but some users have reported that renaming the folders back to their original names after 30 days brings back the rollback option, which you'll find in Start > Settings > Update and Security > Recovery.