HTC HD2 User Manual page 85

Chapter  Using the Home Screen 
In Day view, tap an appointment to view complete details of that
appointment. On the subsequent screen, you can tap Menu to choose
whether to edit or delete the appointment.
When in month view, swipe your finger up or down the screen to
display the next or previous month on the calendar. You can also tap
the Up and Down arrows that appear on the left and right sides of the
month.
To change between different calendar views
On the Calendar tab, tap Menu and then choose whether to display
the calendar in Agenda, Day, Week, Month, or Year view.