I have been wanting to upgrade and I was wondering if I just add a amp will that be enough or do I need to replace the speakers mine is a 03

 

You will likely get a better response in the Electronics Forum.

However, there are people that have added an amp to the factory HU. The '03 speakers are better than the '00-'01 speakers, however IMHO I would also replace the speakers. I would also run better wires to them. If you saw the factory wiring you would wonder how it works at all! It is VERY thin wire.

If you are going to all that trouble of rewiring a speaker, it seems almost silly not to replace the speaker.

 

thank you