Next to the Advance Warning is a box for the Recurring Interval. That is the frequency that the event reoccurs (if it does reoccur). For a birthday, enter 1 year. By entering 1 year, after you are reminded of the birthday, the Save dialog will automatically increase the event date by 1 year (you could do this manually even if you hadn't entered a recurring interval). Pop-up menus are used to set the Advance Warning and Recurring Intervals to days, weeks, months, or years. To use the pop-up menus simply hold the mouse down on the current setting of days, weeks, months, or years and then move the mouse to the desired choice while holding down the mouse button.
-- Changing or Deleting Reminders --
In the main window, click on the reminder which you want to change or delete and then choose "Change Reminder" or "Delete Reminder" from the "Reminders" menu. You can also use the shortcut of double-clicking on the reminder in the main display window.