If your Samsung Galaxy S II is slow, or it freezes sometimes the best thing you can do is, reset it back to the factory setting. If you want to claim warranty repairs, (after rooting), then you must reset the phone before you send it to the provider. This process is sometimes called hard reset.
Once you reset it , the phone will be back to what it was the day you bought it.
Follow the following steps to do a factory data reset.
(PLEASE NOTE YOU NEED TO BACK UP YOUR DATA BEFORE YOU DO THE RESET)
1) Go to settings in your phone.
2) Tap on Privacy.
3) Select Factory Data Reset
4) Select Format USB Storage if you want to format that as well.
5) Then tap on Reset phone.
6) If the password is required, enter the password (your Samsung account log in password)
7) Then select Erase Everything
If your phone is frozen then you will not be able access these option. In that case follow the following steps
1) Switch off the phone (if not possible to switch off using power button, take the battery off)
2) Take the battery off and put it again.
3) Press and hold the volume up button + Home Button + Power button.
4) Once the start up logo appears, release all buttons.
5) Select wipe data./factory reset. (use volume up/down to navigate and home key to select)
6) Select delete all user data and reboot system.
You also can hard rest using the dial pad. Dial *2767*3855#.
