Did you make any other changes other than rooting it?
If not, then you can follow the steps below:
- open the terminal app
- you should see a $ symbol, now do the following
- su
- now you should see a # symbol
- mount -o rw,remount -t ext3 /dev/block/mmcblk1p21 /system
- rm /system/app/Superuser.apk
- rm /system/bin/su
* rm /system/bin/busybox
- mount -o ro,remount -t ext3 /dev/block/mmcblk1p21 /system
- reboot your phone. Toda, no more root
- Complete a factory reset to clear all your personal data and apps you've installed off it
If you've installed a ROM or theme, then you'll likely need to apply and SBF file...