Generally, about 3 inches of non-clumping clay litter, or 1 – 2 inches of scoopable litter should get the job done. Some say less, some say more. Only you and your cat will know the correct amount.
Remove solid, waste at least once per day and conventional, non-clumping and scoopable litters alike. Replace the entire contents of non-clumping clay weekly. And remember to replace the clumps you removed with fresh to keep the level up.
Wash the litter box with soap and warm water and rinse well every time you change litter completely. Box liners are great for helping make litter box maintenance a bit more carefree.
Your cat may not like new litter, so go slow. Mix the new litter in with the old in a ratio of about 1/3 new to 2/3 old. Increase the new litter gradually until you have a total switch-over.