Your car is a 2003. DO NOT pull the plastic covers that go over the speakers to take them off. They will NOT go back on if you do that. Only 99-01's were able to be taken out that way I think.
The proper way to take out the speakers is to put the seats down (via the black straps in the trunk), then you have to take off the side pads of the top part of the seat. It's a 15mm bolt IIRC, if not 14, which is hidden towards the bottom of the pad. You have to hunt for it on the bottom portion of the seat. Afterwards, you take off the C pillar covers and then pop off the panel clips that hold the dark gray/black trim piece where the seats latch. Once that is off, the rear deck dash comes off, you just lift it up.
The speakers are held in by plastic clips. They are not bolted down to the car. Press on the clips and push them up. Then the speaker comes out with the housing around it. There's more clips that hold the speakers in. Push them out with a flathead screwdriver and pull the speaker up. It helps if you navigate the screwdriver in a way where the speaker goes up as the pin is pushed out. Then just pop the new speakers in. You have to angle the speakers so it goes into 2 of the pins that hold it in, then use the screwdriver to push the other pins out and pop the speaker into place. Then put the housing back in the rear deck and reverse the steps.
You will also need a speaker wire adapter, similar to those that are used in the radios.
They look similar to this.
