If you can do it in chunks you minimize the possibility of a cycle, but that may not be pactical for you. If you can take out a third or quarter at a time then add the apropreate amountof new material you shuld not have any trouble.
We Stared out with what we called the Cory's beach, and it gew to encompass the entire tank a bit every few weeks.
90 Gal perfecto with fake plants, eight neon tetras, eight cardinal tetras, four delphax corydoras, four paleatus corydoras, six otocinclus, endlers, and endler fry.
18 Gal hagen Fred the Fancy Guppy Memorial Hospital Tank