To change your mobile device in Duo you will need to open an application that requires a Duo login(ex: MyClasses, Gullnet).
After entering your user name and password you will be prompted for Duo verification.
At the Duo Authentication screen select My Settings & Devices
Choose Enter a Passcode and you will see a prompt below in blue to select Text Me a New Code.
You will receive a text from DUO with a long list of numbers.
Enter the first number received by text, starts with a 1 and ends just before the comma, into the field provided and click Log In.
Select Device Options in blue next to your device phone number.
Select Reactivate Duo Mobile to have your new device activated using the same mobile number.
Choose the device type as either Iphone, Android, etc.
A bar code will be presented on screen.
Go to the Duo Mobile App on your device and press the + button to scan the bar code.
Once you receive the green check mark your device is now reactivated for Duo Mobile press the continue button to continue with logging in.