Note: Just ensure to back up all of your important data stored from the phone, for this will wipe it all out and clear you device and stored back again like the first time you bought it.
The factory reset method:
Factory reset - this is only a soft reset method, you can do this if the device is still active or you can still navigate to it's menu and settings function.
- Tap the Menu key
- Tap Settings
- Scroll down to and tap Privacy
- Tap Factory data reset
- Tap Reset phone
- Tap Erase everything.
If the Samsung Galaxy S Plus I9001 is frozen or stuck on boot or hangs on welcome screen logo only. This time you will need to hard reset it by way of button combination since you cannot do a factory reset from the instruction above.
- Turn your Samsung Galaxy S Plus I9001 off, or remove the battery for about 10 seconds then put it back again.
- Then press and hold the following buttons Home button + Volume up + Power button.
- Then a menu will show, just select Wipe Data/Factory Reset.
image source: gsmarena.comhttp://www.gsmarena.com/samsung_i9001_galaxy_s_plus-pictures-3908.php