To upgrade an android device, you have two options; you either wait for the phone manufacturer to push the updated version of the ROM for your device to it or, you may download an upgraded custom ROM from the internet and flash it on the phone. Either ways, your android device would be upgraded however, waiting for the manufacturer may take forever and this is the reason you might prefer the custom ROM.
Before an android device could be upgraded by a means of custom ROM, that particular android device has to be rooted or have an unlocked boot loader.
Why Root or Unlock Boot loader Prior to Upgrade?
Your android device has to be rooted or have its boot loader unlocked before you can be able to upgrade it by means of custom ROM only for one reason; custom recovery
Custom Recovery is the access room for unlimited personalization and better performance for your android device but the Root Access and the Boot loader are the only keys to this room; the Custom Recovery.
So, to be able to flash a Custom Recovery on your android device, you need to either Root the phone or unlock its Boot loader
How to Flash A Custom Recovery On Android Device
To flash a custom recovery on an android device, you have two known means to do that;
1- By Means of Root Access: if your android device is rooted, you can simply do a search for " recovery tools " from the Play Store and select from the results the search brings. You should be able to find an app that will help you flash custom recovery on your android device from the Play Store. Most of these apps can detect your phone model, download a custom recovery.img file for you and flash it directly. Or, alternatively, you can download custom recovery.img file for your android device from here and choose the " Other " option from any of these apps to flash the recovery.img file you may have downloaded.
2- By Means of Unlocked Boot loader: this method requires your PC and that you have a fair knowledge of Command Prompt and ADB Command lines. To learn about the ADB Commands and how to set it up, click here.
Once you have unlocked the boot loader of your android device, simply download the recovery.img file for your android device and place it on the same folder as your ADB Tools. Then, do the followings;
i- On your phone, go to Menu<<>>Settings<<>>Applications<<>>Development (for android 2.3 downward) and Menu<<>>Settings<<>>Developer Options (for android 4.0 upward) then, enable USB Debugging on the phone.
ii- Download and install the specific android drivers for your phone on the PC.
iii- Now, connect the phone to the PC and wait patiently for the PC to detect and install the phone's drivers. You can now open command prompt and point to your ADB Folder from the command prompt by typing " adb cd c:\adb ".
iv- On the command prompt, type " adb devices " to confirm that the PC has connected to your phone then; type " adb reboot bootloader " ; the phone should shut down and reboot to bootloader.
v- Now, wait few seconds for the PC to install the phone's drivers again then, type " fastboot devices " on command prompt - this is to confirm that the PC is still connected to the phone.
vi- And finally, type " fastboot flash recovery recovery.img " and wait for the process to complete.
Pro Tip: You should rename the recovery.img file you may have downloaded for your device to: " recovery " otherwise, the PC won't recognise the command line. And DO NOT tamper the .img suffix of the file.
Congratulations! You now have custom recovery flashed on your android device. You can now proceed to flash any ROM or MOD and enjoy your android device like never!
How to Unlock Bootloader or Root your Android Device
To unlock your android devices' bootloader, you may have to refer to the manufacturer's support page on their website or do a Google Search for your device.
As for the root access, there are several procedures for rooting an android device and NOT all the methods work for all android devices so, you have to look for specific method that works for your particular device.
Also, you may refer to this page for a detailed info on how to flash a new ROM on your android device.
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