It is easy for students to join a new class using a class key. In the left menu students click "Classes" to see the classes that they currently belong to. There will also be the option to join a new class. Click "Join New Class" and enter the class key. The student will automatically be added into the new class roster.
If a student is activity working in a lesson in the code editor, they will need to click their name in the upper right corner to navigate to their dashboard view with the left side menu bar.
Note: If you are moving a student to a new class, you can delete the student from the old class roster.