All you have to do is by new speakers. Most speakers connect to the component with any plugs. If the component isn't damaged, then just go and price some new speakers.
I am in the process of replacing the factory speakers in my wife's 2002 Liberty. Unfortunately, the deck does not drive the speakers, there are small amps in each of the front door speakers. Therefore, you cannot replace them with aftermarket speakers unless you replace the deck as well. The other option is to replace them, add an amp and rewire the entire system. This is not what I bargained for when I started this project but in the end it will be a lot better system then the factory system.
6.5 in front and 4x6 in back
Walmart.com and others sell a speaker spacer that should work.
Which speakers are you trying to replace? Front or rear?
Fronts are 4.75 with a 1" tweeter the crossover is hard wired into the car and made for those stock speakers. If replacing speakers run new wires, using the old ones will split your audio for the factory component system it is not recommended for use with any other speakers. The rears are 10 ohm replace ASAP. Not sure of the size may be 5*7 or a small 6*9
3.5"-4" in the dash and 6"-6.5" in the front door. To remove factory door speakers, you will have to drill out the rivets. To replace door speakers, you will have to fabricate a spacer ring or find one to purchase (door is very shallow).
It is a relatively easy job to replace your speakers depending on where they are located.
To replace the back speakers in a 2006 Acura TL, remove the SRS housing on both sides and the back panel of the speakers. Remove all wiring attached to the speakers and replace.
Pretty much any kind you can afford and install.