How do you turn a aggressive cat into a passive cat?

With a lot of time and patience. Never punish the cat, as this could make the aggression worse. Neutering also helps calm a cat down.

Take a look at your cat's behaviour. Does it become aggressive at a certain time, or when you do something specific? Some cats do not like being picked up, stood over or even approached. If this is the case, let the cat come to you in its own time. It should eventually learn that coming to you is a positive and rewarding experience.

Has anything changed in the household recently? Many cats don't like change, and the uncertainty could make some cats a little aggressive until things have calmed down and they feel safe again.

If this is not a new behaviour, then it could mean the cat has had a troubled past, or was taking from its mother too young. Kittens learn social skills from six to twelve (or more) weeks old, so leaving mother at this time would mean the kitten has not had all the social lessons it needs to learn. This can manifest as seemingly unprovoked biting, scratching and other behaviours - because the cat does not know any better.

There are many, many reasons why a cat may be aggressive. The first port of call is always a checkup at the vets. A sudden change in behaviour usually means a medical problem. A cat behaviourist could also work well, and help you find the root of your cat's problem.