1.  Back up your device. Because your phone isn’t rooted yet, your options for backing it up are limited. I suggest using MyBackup Pro, which is $4.99 on the Android Marketplace but has a 30 day trial, which is all you need. We will be performing a much more thorough backup later once your phone is rooted.
  2. Install the P999 drivers on your PC. They will allow your phone to connect to your PC.http://www.lg.com/us/support/mc-support/drivers/LG_T-Mobile_Android_USB_Driver_v2.2.zip

  3. Download SuperOneClick.

     Download SuperOneClick.

    Download SuperOneClick. SuperOneClick is a program that allows you to easily root your phone. Unpack the zip file and copy it to your desktop. NOTE: The file may be flagged by some anti-virus programs as it uses the same exploit to root your phone that an Android virus did.

  4. Set your phone in USB debugging mode. See step 9 for information on how to do it.

  5. Root your phone. This will void your warranty, so if something goes wrong you can’t return your phone. Make sure USB debugging is still enabled in your phone’s settings and connect it to your PC using the USB cable. Do not mount the SD card.

  6. Open SuperOneClick. Click the Root button. It will now check for your phone and root it if the drivers are installed properly. If this does not work, reinstall the drivers and make sure USB debugging is enabled on your phone.

  7. Back up your device again. Now that your phone is rooted, you can perform a much more thorough backup of your device using Titanium Backup. It’s free on the Android Market, so search for it and select “Download”.

    • If you would like to support the developers and get some more useful features, you can buy Titanium Backup Pro instead.
  8. Enable USB Debugging.

     Enable USB Debugging.

    Enable USB Debugging. Titanium Backup will not work properly without this enabled and it is required for later steps. Go to Settings > Applications > Development, and select the “USB debugging” checkbox. Read the warning and select OK.

  9. Open Titanium Backup.

    Open Titanium Backup.

    Open Titanium Backup. Press the menu button on your P999 and select “Batch”. A screen with a lot of options will appear. Select the button beside “Backup all user apps + system data” that says “RUN”. Make sure “Kill active apps” is selected and press “Run the batch operation”. It will take a few minutes to complete.

  10. Copy the backup files somewhere safe. You can find where Titanium Backup saved the backup files by pressing the menu button, selecting “Settings”, and scrolling down to “Backup folder location”. You can either copy these files to your PC or an external SD card.

  11. Download your ROM of choice. There are many out there but it all comes down to personal preference. I use Weapon G2X. Make sure you get the P999/G2X version of your ROM, or it will not work. Copy the zip file onto your phone, and leave it packed.

  12. Install ROM Manager. This is a useful app from the Android Market that will allow you to easily boot into ClockworkMod Recovery to install your new ROM. Open it.

  13. Select "Flash ClockworkMod Recovery".

     Select “Flash ClockworkMod Recovery”.

    Select “Flash ClockworkMod Recovery”. Scroll down the list of phone models until you see “LG/T-Mobile G2X”. Select it and allow it superuser permission if prompted.

    • NOTE: This will only temporarily install ClockworkMod Recovery. You will NOT be able to boot into it without going through ROM Manager again. Attempting to do so will instead perform a factory reset!
    • If you would like to install it permanently, follow the instructions here: http://forum.xda-developers.com/showthread.php?t=1056847
  14. Select “Reboot into Recovery”. This will shut your phone off and start ClockworkMod Recovery.

    • You can navigate up and down with the volume buttons and select options with the search button.
  15. Select “backup and restore”, then “Backup”. This will backup your current ROM onto an SD card or PC.

  16. Wipe the cache partition, the dalvik cache, and finally do a factory reset.

    • The “wipe data/factory reset” and “wipe cache partition” options are found on the main menu, while “Wipe Dalvik Cache” is under “advanced”.
  17. Flash the new ROM. Select the “install zip from sdcard” option on the main menu, then “choose zip from sdcard”. Select the ROM you downloaded and put on your phone.

  18. Reboot your phone. If the flash was successful, it should boot up into the new ROM.

  19. Restore your application backups.

    Restore your application backups.

    Restore your application backups. Download Titanium Backup from the market and copy the backup files back to your phone. You will have to change the settings in Titanium Backup so that it knows where your backup folder is. Press the menu button on your P999, select batch, and scroll down to select “Restore missing apps with data”.

    • It is not recommended to restore all your setting backups as this can cause problems when using a new ROM.