If you plan to sell your Samsung Galaxy S2, you will need to reset it to its factory settings. A reset can also help you resolve issues with malfunctioning phones. When you reset the Samsung Galaxy S2, all data on the phone will be erased, and if you choose, it will also delete data stored on the SD card, including installed apps, app data, and settings, as well as the Google accounts linked to the device. However, it won't remove the current operating system, integrated system apps, or any data stored on the external SD card.
Steps
Reset Using the Settings App

Open the 'Settings app'. On the home screen, press the Menu button and select the 'Settings app' to open it.

Begin the phone reset process. In the 'Settings app', select 'Privacy', then tap 'Factory data reset' to restore the phone to its factory settings.

Choose whether to erase the internal SD card. On the 'Factory data reset' screen, you can decide whether to erase data on the internal SD card or leave it intact. Check the 'Format USB storage' option to select or unselect it.
- If you check the box, all data on the internal SD card will be erased.
- If you leave the box unchecked, data on the internal SD card will remain intact.

Reset the phone. Once you reset the phone, you will not be able to recover the data on the device. Tap 'Reset phone', then tap 'Erase everything'.
- The Samsung Galaxy S2 will begin the reset process. Do not turn off the phone while the reset is in progress.
Perform a Hard Reset (Using Hardware Buttons)

Try resetting using the 'Settings App' first. If, for any reason, you can't reset the phone through the Settings app, you will need to perform a hard reset. This means you'll use the phone's hardware to reset it, instead of the software.

Turn off the phone. The power button is located at the top right of the phone. Press and hold the power button until you see the options screen. Tap the "Power off" button to turn off the phone. Wait until the phone completely powers down.

Turn on the phone using the power and volume buttons. The volume buttons are located on the left side of the phone. While holding the volume up/down button, press and hold the power button. When the Samsung logo appears, release the power button while continuing to hold the volume button. When the Android "System Recovery" screen appears, release the volume button.

Reset the phone. Use the volume buttons to navigate to the "Wipe data/factory reset" option, then press the power button to select it. Press the volume down button to highlight "Yes - Delete all user data", then press the power button to confirm. Press the power button again to restart the phone.
- The Samsung Galaxy S2 will begin the reset process. Do not turn off the phone during the reset.
