To promote students of a class to the next class, you need to use the Student Module which can be accessed via the Menu Bar located at the top right of the screen.
Step 1. Click on the Student Module under the Menu Bar.
Step 2. Click on Student Promotion on the left sidebar of the screen. 
Step 3. Select the class, whose students are to be promoted to be next class, by selecting the Academic Session, Batch and Class. 
Step 4. Select the students which are to be promoted. 
Select 5. Select the class to which the students are to be promoted, by selecting the Academic Session, Batch and Class. 