It is recommended to back up all necessary data by copying any files you want to save from your phone to your computer. WARNING!!! A hard reset restores the original factory settings and may erase all downloaded content, including images, ringtones, contacts stored and programs installed in the internal memory. You can use a USB data cable to connect your phone to your primary computer, and use Zune to restore your backed up content and the earlier version of your phone software.

Hard Reset Nokia Lumia 710

To hard reset you Nokia Lumia 710, follow below instructions:

From the Start screen, swipe left.
Tap Settings.
Tap about.
Tap reset your phone.
Read the warning about all personal content being erased.
Tap yes.
Tap yes again.

Here are two other methods

Method 1
From the main menu either swipe right-to-left on the touchscreen or press the right arrow button on the top right of the interface.
Scroll through the icons until you get to the ‘Settings’ menu. Then, tap the ‘Settings’ icon.
Scroll down to the ‘About’ menu which should be second from the bottom. Tap it.
Press the ‘Reset Your Phone’ button.

The phone will reset itself and return you to the main menu.

Method 2

Switch the phone off.
Press and hold the Volume Down, Power and Camera buttons at the same time.
When the phone vibrates release the Power button but keep the Camera and Volume Down buttons held for a further five seconds.

The phone will now be reset.