There are a couple of options for de-worming. A “spot on” solution and a worming tablet. You need to check which type of worms they kill as some only kill one type of worm (which may not even be the worm your cat has!). For example, some only kill tapeworms and some roundworms etc. Most worming treatment should be given as a preventative every 3 months, but check with the product and your vet.
Tablets
In my opinion, tablets are better for worms than spot on. Although, they can be harder to give, especially to adult cats or feisty kittens! Tablets can be crushed up and mixed with food, but many cats can smell them still! There are also treats called “easy pills” which are shaped so you can pop the tablet inside and the cat eats it with the treat.
Spot on
Spot on solution is given on the back of the neck, like the flea spot on. This could be easier to give, but depends on your cat – mine freak out when they see the tube of flea liquid!