Leaving a Graduate Program in a Polite and Professional Manner
This goes the same for those leaving jobs for similar reasons- the more you can explain how there are personal reasons for your transfer and do not emphasize that there are deficits with your current program, a professional academic will understand even if he or she is disappointed. 

Remember that not all academics and administrators are always professional and that despite your best efforts he or she might not be understanding. However, being professional and cordial is the best you can do to take the high road.