Advice needed for Honda ep3

[BlueBullet02]

I have a Honda SE 1.6 btec 3-door hatchback ep3, and I would like to upgrade my sound system/speakers. It’s a 2004, so the sound is terrible with no good bass or crisp audio.

I know for a fact the wiring has been re-done, so I just need to know how to figure out what speakers/sound systems are compatible with my car, please can you help me find out how to figure this out? Or if you have specific recommendations, something like JBL or Pioneer would be great. Thank you!🙏🏼