Removal Procedure

Raise and support the vehicle.
Use a utility stand to support the catalytic converter.
Disconnect the oxygen sensor electrical connector.
NOTE: To prevent internal damage to the flexible coupling of the catalytic converter assembly, the converter must be supported. The vertical movement at the rear of the catalytic converter assembly must not exceed 6 degrees up or down.
Remove the catalytic converter nuts from the exhaust manifold.
Disconnect the catalytic converter from the catalytic converter hangers.

Fig 1: Removing Catalytic Converter Nuts From Exhaust Manifold
Courtesy of GENERAL MOTORS CORP.
Reposition the exhaust system in order to access the exhaust seal.
Remove the catalytic converter seal.

Fig 2: Removing Catalytic Converter Seal
Courtesy of GENERAL MOTORS CORP.