The option to switch classrooms is located on the "Teacher Select" screen. From there, you just tap on the teacher's name to switch to that classroom account, and all of their student profiles will be available.
To switch classrooms on an iOS device:
If you are on the Educator's profile screen, tap "Change Teacher." If you are in any profile, go to the profile settings, (the gear icon), tap "Sign Out" of Epic! Account and tap "Switch Classroom" to get back to the "Teacher Select" screen.
(When Epic! times out after 5 minutes of inactivity, the app will default to the "Teacher Select" screen)
To switch classrooms on the website:
Click the menu option (3 white lines, top right corner), then click "Switch Profiles" in the drop down menu. On the profile chooser screen, tap the "Sign Out" button and this will take you to the "Teacher Select" screen.