I just did the opposite, I went from fine sand to a coarse grain sand. I took half of the sand out and replaced it with the new sand. I removed the old sand a little at a time over the course of a week, one section at a time. I used a small plastic container to scoop it out. Then I add the new sand, about 1/4 inch every week untill I got where I wanted it. I used a 2' piece of 2'' pvc with a funnel on top to add the sand. I used this long drawn out method to replace the sand because I didn't want to stir up nasties from my 4 year old sand bed. but I did. I got a nasty diatom bloom and some other algea problems going on now that I never had before. everything was fine untill I messed with the sand. so be carefull, take your time, maybe even longer than I did. good luck