sand issue

Ok so I have a 150 gallon tank.I lost almost everything a few months ago due to ick.only thing I have left is one yellow tang, a few starfish,snails,crabs.my issue is when I first set the tank up almost 2years ago I went with playground sand from home depot.I have learned my lesson and now am considering replacing it with the correct sand.But I don't know how to approach it.should I take the fish out and do it all over again. or should I buy the wet live sand and do a slow switch.Orr should I just leave it alone.....I'm bouncing back and forth here I don't know what to do.and I don't wanna lose my last tang.