Reasons for this might be that you just don’t get on with any custom ROMs, or perhaps you want to sell the device as it was when it was new.
Sometimes if there is a limited development scene for a device, custom ROMs might be missing a feature that you liked on the standard ROM – in which case one solution is to cook up your own ROM with it baked in. Alternatively, you may want to restore it back to the stock ROM.
When rooted, most devices allow for installation of ClockworkMod or another custom recovery solution. When rooting your device for the first time, it’s strongly advised to make a backup of your current ROM, just in case of any problems that may occur or if there is data on there you may need later.
Using ClockworkMod makes backing up and restoring ROMs an absolute breeze, and this guide will take you through using ClockworkMod and restoring.
But what if you forgot to run a backup before installing a ROM? Luckily, there are other solutions available for getting your phone back to its original state.
The easiest involves downloading an RUU (ROM Update Utility) from the manufacturer’s website for your device, but these are not always available so we’ll show you an alternative method.
Go back to your stock ROM by restoring from the backup that you made when you rooted your device (if you didn’t do this, skip to step 4). Boot into recovery from within your ROM, or by holding down the volume button when you boot up.
2: Wipe old ROM
Before installing a new ROM wipe everything on the device, except the SD card. This is done within ClockworkMod by clicking ‘Factory Restore’ and choosing the ‘Wipe Dalvik Cache’ option within the Advanced menu.
3: Restore stock ROM
Once you are in recovery, navigate to ‘Backup and Restore’ then Restore. You should see a list of your backups by date. Tap on the one that corresponds to your standard ROM. The device will then be restored.
4: Find stock ROMs
If you didn’t make a backup of your stock ROM, there are stock ROMs available to flash in the same way as you would a custom one. Navigate to XDA (http://bit.ly/a5dqD ) and choose your device from the list.
5: Choose ROM
Once you have found your device on the website, enter the ‘Android Development’ section for it. Quite often, stock ROMs are stickied to the top. You are likely to have a choice of rooted or unrooted stock ROMs.
6: Download ROM
Once you’ve chosen your ROM on the XDA website, copy it to your SD card by mounting the SD on your computer and dragging the ZIP file to it. Unmount the card and reboot into recovery mode. Do a factory reset and wipe the Dalvik cache.
7: Install stock ROM
Choose ‘Install zip from SD card’ and then ‘Choose ZIP from SD card’ before selecting the ZIP file from your SD card. Click on the file, then choose Yes to confirm. The stock ROM will then install in the same way as a custom ROM.
8: Back to square one
Once the stock ROM has installed, reboot and you should see the device as it was when you got it. Note that if you chose a non-rooted ROM then you will have lost root permissions and will need to re-root.
9: Installing from RUU
If there is no stock ROM available for your device, you can try getting an RUU for it from the manufacturer’s website. This is an executable file that you run on your computer rather than on the phone to install a ROM.
10: Run RUU
Most RUUs are not rooted and some may not support a custom bootloader if you installed one on your phone. All update processes differ, but most involve doubleclicking the RUU with the phone plugged into your computer.
How to Reset an Android Phone to Factory Default
Source : Android Tips, Tricks, Apps and Hacks