If the date and time for a booking needs to be changed, you should click the small wheel icon, which you find next to the Start Lesson button under My Lessons. This will then show you 2 options: 

Cancel lesson or Reschedule Lesson.

You should only Cancel the lesson in case you never want to teach the student the lesson.

If you rather want to re-schedule the lesson to another date/time you hit the " Reschedule Lesson " button. 

You find this option by rolling with your mouse on the left side of the " Start Lesson " button at https://www.playwithapro.com/mylessons - under the " Upcoming lessons " section. That will reveal a small gear icon- which when clicked - reveals 2 options- either to Cancel the lesson, which refunds your student 100% the amount he/she paid for the lesson, OR you choose to hit the re-schedule button and then choose a new date/time. Re-scheduling will keep the students money in the system and like so there is no need for the student to make a new purchase. 

See below where you find the options.