The whitening gels we use to whiten teeth only work on natural teeth and have no effect on porcelain surfaces.
If you have crowns now, you can’t go back to veneers. Plastic fillings and bonding technically do not respond to the whitening process. I say “technically” because if the bonding is thin enough, it will seem as if the tooth has lightened when the lighter tooth surface will show though.
So the answer is “yes,” you do need to replace your crowns if you want them to match your whiter teeth. However, I would do this after you whiten your teeth so that your dentist knows the exact color to match to. Wait two weeks until after you are satisfied with your whitening before replacing your crowns.
Mark Burhenne DDS