It’s pretty simple really. It’s basically the reverse of what you do if you’re impatient and can’t wait for an update to arrive: you force it manually. While some devices, like Samsungs running Knox, don’t let you easily downgrade, Nexus devices are different: you’re free to do whatever you choose whenever you like. So how do you do it?
First up, you need the factory image for the Android version you want. In this case we’re going to use Android 4.4.4 KitKat for the Nexus 5 – but you can substitute any Nexus device and any Android version you like. If you want to downgrade a Nexus 4 to Android 4.3 Jelly Bean you can do that too. As you can probably guess, this process will wipe the contents of your phone clean, so make sure you have a backup of your apps and data before proceeding.
How to downgrade a Nexus
1. Once you’ve got the factory image on your PC, you want to download ADB Tools (if you don’t already have it) to your PC as well.
2. Move the factory image file into the ADB Tools folder and unpack it.
3. Make sure USB Debugging is enabled on your Nexus. If it isn’t, go to Settings > Developer Options and check the box next to USB Debugging. If you don’t see the Developer Options section, go to About Phone and repeatedly tap the Build Number until you see the notification pop up. Then back up to Settings and you’ll see it at the bottom. Now, check USB Debugging.
4. Turn your Nexus off.
5. Press and hold Power and the Volume Down button to enter Fastboot mode. If you have a custom recovery installed you will be able to use the volume buttons to select Recovery Mode and press the Power button to confirm.
6. If you’ve got stock recovery, when you see the Android chilling out on its back, press the Power button and quickly press the Volume Up button to enter Recovery. From Recovery Mode you navigate with the volume buttons and confirm with the Power button.
7. Scroll down to ”wipe cache partition” and hit Power to confirm.
8. Scroll to wipe date/factory reset and hit Power to confirm.
9. Now, connect your Nexus 5 to your PC with a USB cable.
10. Open up the ADB Tools folder and find thefile and double click it. Once it has done its thing your Nexus will reboot with whatever version of Android you just flashed on it.. Proceed through setup and restore your apps and data to enjoy the KitKat fun once again.
Note: Of course, once you’re back on KitKat, you’re going to get over-the-air update notifications. You can simply ignore these