The first thing you want to do is put the car on jack stands so you can fit under the car. Remove any heat shields that may be connected to the front of the exhaust right behind the exhaust manifold. The catalytic converter looks like a rounded box connected just behind the exhaust manifold and you should have one on each side on a v8 or v6. Spray penetrating oil on the bolts and remove them with a socket. You may have to use a hammer to loosen the converter from the exhaust but be careful that you don’t damage the exhaust system. Install the new converter, you may need help holding the converter while you reinstall the bolts. Reinstall the heat shields if installed and start the car to check for leaks. if you discover a leak it is most likely due to a loose bolt. You are done now go out and have fun.