hi forby - i did the opposite, i have a very large tank, and went from sand, to coral sand, i didnt take the fish out, i just lifted out the sand using various things....not easy with sand, bit by bit i got it, then i used a hose pipe 'which i use to do water changes' and just hoovered the last bits up, then after cleaning the coral sand, i just put that in.......75kgs of the stuff!
not sure what the exact procedure is, however this worked for me and no fish died
me personally would just use a net and/or another tool, to scoop out the coral sand, the fish will just go to the other side and think you have gone mad, then just scrape over the rest and lift from the same spot - after you drop your sand in, it will potentially go milky for a couple of days, but the fish should be ok...ive done this myself on another tank, but each to their own....good luck buddy anyway