You cannot install an aftermarket catalytic converter on a car when the current converter is still functioning properly, or the replacement is under warranty or recall.
If you want to know how to use aftermarket catalytic converter to increase performance, you need to look at the entire system. Many people think that installing an aftermarket converter will give them significant performance enhancements. However, there are other less costly changes you can make that will give you bigger impact on your performance. You can add a cold air intake or a street header and get more impact. You might also consider a to reduce pressure inside the catalytic converter. All of these have a lower cost than a converter and give you more impact.
Installers of aftermarket catalytic converters are required to complete a warranty card in triplicate with the original going to the customer, one copy to the installer, and one copy to the manufacturer of the converter.