You can change the role of an invited teacher by following the steps below. 

For mobile:

1. Open the class where the teacher is located
2. At the bottom right corner, press the Members tab
3. Press the teacher's name for which the role needs to be changed
4. Press Options in the top left corner
5. Click Edit Role
6. Change the role to your liking 
7. Click Done
8. The invited teacher's role has been changed!

For desktop:

1. Open the class where the teacher is located
2. Along the top bar (Updates, Calendar, etc), click the Members button
3. Click the teacher's name for which the role needs to be changed
4. Click Options in the top left corner of the box
5. Click Edit Role
6. Change the role to your liking 
7. Click D
8. The invited teacher's role has been changed!