If you find detritus in your sand at all, I would slowly remove the existing sand bed vs trying to clean it. When you are done (a few weeks), replacement is optional and inexpensive.
-Matt
There is no reason to replace the sand.
All he has to do is at every water change use some sort of a gravel vac and use it and clean part of it each time.
If you haven't ever done it before, I'd only do about 1/2 at a time.
I find detritus all the time in my sand. Detritus happens.