How to Uninstall Windows 10 Mobile Preview?

Testing new OS is fun! May it be mobile OS or computer OS. But this time, my expectations are way too high which made my Windows 10 mobile preview experience a little bit boring. I didn't spend much time to explore it due to the bugs that made the device almost unusable. Since Windows 10 mobile is still being tested, I already anticipated those bugs prior to upgrading so there is no reason for me to complain. Maybe it's too early to have it on my device since the rumored official release of Windows 10 mobile will be on the last quarter of this year. There is still a lot of time to improve the OS. At this current build which is 10149, the experience is almost similar to iOS 7 beta 1 when Apple made its major overhaul to iOS. It's almost unusable. Although the user-experience varies per device, my experience using Windows Lumia 640 is not that functional compared to my previous testing experiences. You cannot use it yet as your daily driver so don't install the preview on your main smartphone. If you want to continue playing with Windows 10 mobile OS, install it on your secondary device. But don't fret! Windows 10 mobile preview build number 10149 works best on other windows devices with higher specs. Just try it of you have those devices!
In case you no longer want to test Windows 10 on your device because you find it very slow, you cannot reset your phone to factory settings of Windows 8.1 by simply resetting it on Settings > About > Reset Your Phone because you are actually resetting Windows 10 to it's original settings.
To get out of Windows 10 OS and get Windows 8.1 back to your device, you need to download Windows 8.1 firmware from Microsoft. To do this, download this software called "Windows Phone Recovery Tool"  and install it on your computer. Here's how it works:




Once finished with the installation, you may now enjoy Windows 8.1 OS! Just reinstall everything and I believe you backed up your device prior to installing Windows 10. If you backed-up your photos in OneDrive, you will see it immediately loaded on your device.