If you want to change your Viber number, simply deactivate your Viber account and reactivate with your new number (this restarts the setup process). To do so, go to the "More" tab in the Viber app.

1. Open Viber

2. Tap on the 'More' item in your device's menu.

3. Tap on 'Deactivate Account'

4. Tap on 'Deactivate' when the warning notification pops up.

5. You will receive a verification that your deactivation was successful.

Now reactivate your Viber account using your new phone number. To do so run the setup again. Enter the new number that you'd like to use. This will erase your previous Viber number and replace it with the new one.

http://facebook.com/viber
http://twitter.com/viber