You can change the amount a student pays for lessons by changing the Rate of the student.

To do that, click on Student icon on the left, and then click on the student’s name, and scroll all the way down to the bottom and see the Rate that's assigned to them. Click on the Rate that's there and select a different Rate from the list, then Save the change.

If you need to adjust the the Rate amounts themselves, go to your Settings (Click on your name in the top right of the screen, and choose Settings). Then click on the Rates tab.

From there you can either create a new Rate, or edit an existing Rate by clicking on the blue pencil icon to the right of the existing Rate name you want to adjust.

Here's a video to explain how to do that...

If you find that after setting the attendance, it is still billing them at the old rate by default, you may want to delete the lesson schedule starting on the date of change, and recreate it for that student. If you don’t want to do this, you could also just override the amount when setting attendance, if this is a problem.

If you do end up charging students too much accidentally, the quickest way to rectify the problem is to issue a credit to all the students who were charged an extra amount (you can do this all at once from the Billing → Fees & Credits screen).