Hello MAgyeduD!
Ok, so the process is involved, but worth it. These installation methods should keep your files and apps, but all the same, backing them up would be a good idea.
First things first, you'll want to find the product key of your license for Windows, just in case something goes wrong with the activation, and write it down on paper. You will usually find it:
- On the bottom of your computer
- Inside the box or on the disc you installed Windows from
- You can also download NirSoft ProduKey, a free, temporary, light, and safe tool that detects and displays the product key that your computer is using. (I can't link it directly here for safety reasons, but just Google it)
Then go to the download page here:
https://www.microsoft.com/en-us/software-download/windows10
Everything about this installer takes a long time. Sorry about that. Just wait.
Run the installer and agree to the license. Then click Upgrade Windows. It will download Windows 10, and then ask you to restart.
Be warned that, depending on the age and stability of your PC, it may not work. It might hang, crash, or spout an error code. There are hundreds of things that can go wrong, as the internet will show. Windows will do its best to revert and repair itself upon restart.
Another method involves running the installer, and clicking "Create Media" instead. This requires that you have a completely empty USB flash drive with considerable room on it. Choose the drive, and then it will turn the drive into an installation disk for Windows 10. When the installer was done.
This part is SUPER advanced. Plug the drive in and shut down your computer. When you turn it on and your logo shows, repeatedly press one of your function keys (usually F9, F10, or F12) to open your boot menu. This may take a few attempts to get right; you may need to consult the internet or your computer manual to find out exactly how to open your boot menu.
It should show a list of available devices. Use the arrow keys to select your USB drive out of the list, and press Enter. It should boot to your USB drive, and display the windows 10 logo on the screen with a loading ring. (this takes a while too). When the window appears, follow the on-screen instructions.
This part puts the previous wait times to shame. Once you've chosen your language, chosen the correct disk to install it on (it should be your hard drive), and entered your product key (if the one you have doesn't work, click "I don't have a Product Key"), it will install, restart a bunch of times, and then finally show the lock screen. Remember, once you log in, it will need to download a ton of updates, install updates for UWP apps, run Windows Defender, and index searches, etc.
That's the simple version, but I know a lot more about this process (I've upgraded 8+ computers with it encounting), so ask me if you have more questions, or search the internet)
Disclaimer: I am not responsible for a failed or corrupt installation, or loss of files or operating system thereof.