In the Diary, you can drag and drop appointments to different times within a day, or to a new time on a different day within the same week, you can also use the reschedule button.

To use the reschedule function, click on the appointment in the Diary -> Select Reschedule -> OK -> OK

After selecting the above options, you will see you are in the reschedule screen by the blue notification at the top of your Diary

Click through the Diary to choose a new appointment date and time. Click the preferred date and time to move the appointment to -> This will bring up the appointment in full screen -> SAVE.