There are generally 3 ways to return to Windows. How it will work depends on what you did when you installed Ubuntu. If you still have Windows, and if you can boot on it, then you don't need the steps below (although they would still work too). Removing Ubuntu is a different task than resetting or recovering Windows.
1. "Factory Reset" or "Recovery" is a BIOS-level option you may see when booting the computer. Watch the screen carefully when booting to see some "F-key" (like F11 or F12) that indicates Factory Reset or Recovery before GRUB Menu loads (or before Ubuntu starts). You have to be fast to hit the F-key or it will skip it. Reset/Recovery is stored on a special partition on the hard drive. If you deleted this partition when you installed Ubuntu, then this option is no longer possible.
2. When Windows was still on the computer, you usually have an option to make a "Recovery USB" for Windows. Unfortunately, most people do not make this USB backup. If you did, you can boot the computer on the Recovery USB and reinstall your Windows. Some companies may sell you a Recovery USB if you didn't make your own, but there's no guarantee that you can buy one now. You would have to check the computer company's support site.
3. If you have another Windows computer, or a friend with a Windows computer, you can download the Windows Media Creation Tool and use it to download the Windows 10 ISO and burn it to a USB. With that, you can boot on the USB and install Windows 10. This is not a "factory version" from the computer company... it is the latest Microsoft version. You'll need a 32 GB flash drive and a good internet connection because it is a BIG download, somewhere around 5 GB. I think that older versions of Windows are available too (direct from Microsoft) but you would need the Product Key in order to download it and activate it. If you had Windows 10 before, it will activate automatically after you go online again.
Windows support is not what we do here, but I wanted to give you at least a head start on how to proceed. Use Google to find the Media Creation Tool and where to download the Windows 10 ISO file if this last step is your only option. Only download from official Microsoft websites.
Although Ubuntu did not satisfy your needs, we would encourage you to try other Linux distros if you are willing. There are many of them and we hope that you would find one you like. Ubuntu is popular for beginners, but they have many different versions, so even a different Ubuntu (like Lubuntu or Ubuntu MATE) may appeal to you. But also Linux Mint, Linux Lite, Zorin Lite are all good choices for beginners, and more than those too. Good luck!
