When a candidate decides not to follow-through on a scheduled interview, it is tempting not to show up. However, common courtesy and preserving future employment options with the organization dictate a cancellation notice, according to About.com.
As soon as a person decides to cancel an interview, it is best to communicate that intent. Hiring managers appreciate advanced notice to adjust their schedules.
Decide the method
A phone call or email are common methods for cancelling an interview. A phone call is more personal and is a better option when time is short. An email is fine when the notice is well in advance of the appointment.
A detailed reasons is not typically necessary. It is usually sufficient to indicate a desire to withdraw at this point and thank the hiring manager for the opportunity.