My suggestions for steps to undergo.
Disclaimer: I am not responsible for any damage caused to your persons or vehicle
Get new speakers first. 6.5 inch components SHOULD fit with spacers.
If you still don't like the sound, and you would like to put an amp in, Get a 4 gauge amp wiring (or larger if you want). Wire it into the cabin through the front left footwell, there is a hole into the outer chassis through a plug, (which when removed, makes snaking the cable through a dream. Trust me, i found out the hard way). You will also need a High to low level converter. This will take your speaker output from the headunit, turn it into something acceptable for your amp. Connect Power, Ground and a switched 12v source to the amp, as well as your signal inputs and your speaker outputs.
Enjoy your new system with a stock head unit.