when i change date , count not changed in textbox
Well - that's because you haven't told it to change.
The code you show calls the CountTotal method in the form Load event - and nowhere else. Which means that the SQL is executed only once: when the form is first loaded. Any changes you make via the DateTimePicker do not automatically update the count at all.
You could try calling the method in your
DateTimePicker.ValueChanged Event (System.Windows.Forms)[
^] handler.
But please, don't use the Text property of the DTP to check the DB - use the Value property which is already a DateTime directly, so there is no chance of miscommunication between SQL and your app as concerns data formats!