If you've recently had students join or leave your school, you are able to update your tracker by clicking Edit Tracker Options | Class on the three dots next to the 'Live Tracking'.

Once on this screen, you are able to scroll down to the textbox where you can enter the name of the name of the student that you are looking to add to your class. They will pop up once you begin typing, providing that they have already been added to your school.

Alternatively, you can remove individuals from the class by scrolling down to the Students list section, and clicking the bin icon next to their name.

It is worth noting that you are unable to do this if Pupil Progress is integrated with your school's MIS (Arbor, SIMS, iSAMS etc) - class lists will instead pull through and update automatically.