How to replace a Catalan converter

1st its Catalytic Converter. And it's either bolted into your exhaust system or welded. There are only 3 components other than pipe in the system. The Manifold that is bolted to the engine, the muffler is closer to the end of the pipe. And the Catalytic Converter which is smaller than the muffler between muffler and manifold under the car. Will need new exhaust gaskets if it's bolted. Most likely the bolts are rusted on.

try the Scotty Kilmer way at 1/2 a tank throw in a gallon of laquer thinner. Drive a 150 miles or so and that could burn out the impurities. Or if you can remove it use a heavy soap detergent. Leave it overnight soaking and check it the next day