How do I remedy a P0303-cylinder 3 misfire. And how do I repair on 2004 Kia Spectra

The car is having a hard time shifting, automatic, especially when the ac is on.

Asked by for the 2004 Kia Spectra
Swap #3coil with another cyl.See if misfire followes coil.may want to swap plug as well.
With engine under powered,trans.will seem slugish.