Let me direct you to the Clam FAQ I just wrote for this sight, it should give you some good info on your Clam:
http://thereeftank.com/forums/showthread.php?t=84096
At 4 inches it does not need feeding.
I would move it up a bit every 7 days or so, but give it about 12 days to sit on the bottom and acclimate to your water first IMO.
Don't make the steps to drastic, but don't move it 1/4 inch up either. Moving things around all the time is not great for them either and a 3 step process to final placement is probably sufficant IME.
HTH,
Whiskey