you back to step one.) keep this up until the bottom of the litter box is even with the top edge of the toilet seat.
at first, you cat will be able to step up into the litter box. later it will jump. toward the end, it will probably jump onto the toilet seat and step into the box. that's good when it happens as the cat will get used to being on the toilet seat.
next, put the litter box right over the toilet. you may need to do this in two stages if your cat is hesitant. just put it half way over the seat and wait until it is 