You can edit, move or delete an appointment in a number of different ways.
You can open an existing appointment for editing in two ways: double-clicking the appointment or by right-clicking and selecting "Open". The appointment screen will open and you can modify data. Appointments marked "Completed" will not allow you to update data.
You can move an appointment in two ways. The easiest is to click and drag the appointment to the new location. If the date is farther in the future, you can right-click the appointment and select "Cut". Then move to the desired date and select "Paste". Note that there is no undo and you must do each step one after the other, or else the appointment may get lost from the clipboard (for example, if you open another application and use the clipboard to copy/paste it will overwrite the temporary appointment you copied). You can also expand the appointment time onscreen by clicking the appointment once, then dragging the upper or lower border up/down. Appointments marked "Completed" will not allow you to move or expand the appointment.
You can delete an existing appointment in two ways: right-clicking and selecting "Delete" or by clicking once on the appointment and pressing the delete key. WARNING: There is no undo function (but you will be asked to confirm the delete operation). Appointments marked "Completed" will not allow you to update data. Appointments marked "Completed" will not allow you to delete.