- Download the relevant Android L OS file from Google site (http://developer.android.com/preview/setup-sdk.html)
- Open developer options on your Nexus 5 phone. These options are hidden. So go to Settings > About Phone and then tap on the build number 7 times. Once you have done that, you will find developer options in your Settings menu.
- Open developer options and make sure USB Debugging is ticked.
- Check if your computer has the relevant drivers required for Nexus 5. If not, download the drivers from here and install (http://developer.android.com/sdk/win-usb.html)
- Make sure you have ADB and Fastboot Installed. For this, follow the steps from here (http://forum.xda-developers.com/showthread.php?t=2317790)
- Connect your phone to computer and open ADB (it will open in a command window). Type adb reboot bootloader. Your phone will go into recovery mode. Check the screen and see that for Bootloader status it shows unlocked.
- Most likely your phone will have the locked bootloader. To unlock it, type fastboot oem unlock. Then follow instructions on your phone screen. This will unlock bootloader as well as do a factory reset of the phone.
- Disconnect and reconnect your phone to PC. You may have to go into settings again, reveal developer options and select USB debugging.
- Unzip the Android L file you had downloaded. Create a new folder with an easy to type name like Android and put all the files in it. Then put this folder into Minimal ADB and Fastboot Folder which is in your computer's program folder.
- Hold SHIFT key and right click on the Minimal ADB and Fastboot folder. From the menu, select "Open Command Window here".
- With your phone connected, type adb reboot bootloader.
- Navigate (use CD to change directories) to the folder where Android L files are stored.
- Type flash-all in the command window.
- Sit back and relax. If you have done everything right, Android L will be installed on your phone. It will take up to 10-15 minutes though. The boot part especially takes a lot of time.
Warning: Installing preview version of Android L may void the warranty on your phone or tablet. Also, if something goes wrong during the installation process, we are not responsible. We have used the same method to install Android L on Nexus 5 successfully. And though chances are low, it is possible you may end up with phone that won't boot.
Additional notes: The preview versions are likely to have bugs so once you install the Android L you may find a few things not working in your phone. Installing Android L will delete all your data on the phone, so back up or save photos, music, files or any other data before installing the OS.
Source from TimesOfIndia