Should i change my catalytic converter?

If the code keeps coming back after resetting, you would need to replace it.

Since you had misfire codes previously, give the engine some running and erase the codes and retest.

Just to add to this one more then likely you will have to replace the cat.But like khlow2008 said make sure the missfire is gone and the cat code comes back.

I read that if i keep running the car without replacing the converter then it could back up into the engine and cause damage. I do i know for sure if the converter is bad.

the misfire is gone after changing the plugs, but the cat code came back two times already since clearing them.

in my previous message i meant to ask, how do i know for sure the converter is bad. other than relying on the code.

If your getting that code and there are no exhaust leaks and your 02 sensors are working correctly bad cat.Usually when you have a plugged cat it doesnt set that code.A cat not working correctly emissions wise sets that code.

If you don't have any other codes and has had the vehicle running for some tinme, guess there is no other alternatives but to replace it.

Poor efficiency would not cause any problems but iif the internals becomes cloged badly due to overheating caused by misfires, it can result in loss of perfomance.