Hi Ray, follow these steps to change the Gmail account on your Doro Liberto 810:
1. Go to Settings
2. Scroll down to ACCOUNTS and select the option that says Google
3. Tap the e-mail address shown near the top of the screen
4. Press the menu/options button on your phone (to the left of the Home button)
5. Select Remove account
After you have done the above, go back to Settings and under ACCOUNTS press the button that says + Add account.
Try it and let us know if it works!