If you forget your pattern lock, the only way to access the device is to perform a master reset. Note: A master reset returns the device back to factory settings. It will permanently erase all personal data, preferences, settings and content such as pictures, ringtones and apps that are saved to the device.
To perform a master reset, power the device off.
Press and hold the Volume Down and Power/Lock keys at the same time.
Wait for the screen with the Android images to appear, and then release the Power/Lock and Volume Down keys.
Press the Volume Down key until "Factory reset" is highlighted.