Who To Write To Letter To Get Leave?

Sub: Changing my class timings - Regarding
sir/ madam
      I  want change my class timings 6-7pm to 7-8pm due to the some personal reasons please give the permission to change my timings 
        thanking you
                                                  yours faithfully
                                                  K.Aswini
is it correct way to write a letter to ask permission?