To do a factory re-set please follow the steps below:

1. Press the Setup button on the phone as shown below in red: 

2. Scroll down to the 'Factory Reset' option (or alternatively press 14 on your phones keypad) and choose 'Select' or 'OK'

This resets your phone to the factory default settings. ! CAUTION If you choose factory reset, you will return the phone to the original factory settings and will erase all current settings, including the directory and call logs. It is also possible that your phone extension will change.

3. Once the factory reset has been completed find the IP address from your phone

4. Using the IP address you should now be able to login to the web Configuration Utility page of your phone.