I am going to be changing the sand in my sand filter (because of a wonderful conversion from Baquacil to Chlorine - see more here) and found these words about the steps to do it. Anything to consider besides these points?
To replace the sand in your filter you must first disconnect the pipes going into the valve on top of the filter. Next, unscrew the complete valve counter-clockwise. Once the valve has been removed, you will be able to see the sand bed. The best way to remove the sand is to either use a portable vac or just dip it out with a small can. Once the old sand has been removed, fill the tank 2/3 full of water and just pour the new sand in. DO NOT get sand in the vertical pipe sticking up from the bottom of the filter tank.