This is how I redid the audio on my truck. It had 4 small 4x6 speakers which were almost 20 years old so I had to change that.
The first thing that I tried to do to improve my sound was take the old tape player out and put in a CD Deck. I bought a Pioneer. it puts out 150watts four ways so it was a good one. Then I purchased a Sound Ordnance power 8' sub. and I stuck this under my passenger seat. then on my driver side I have a nob to control the bass. This improved the sound but the highs on these stock speakers cracked and sounded horrid at high volumes. I then wen and took the speakers that were in the dash out and replace them. I bought 2 Pioneer 6x4's thinking they would fit in the dash but they didn't so I had to put them in the door. I had to drill through the fire wall and out to the door and cut out a hole for them in my door. Seeing that I went this far I decided to replace the last two speakers only just this week. The final two speakers are right by my head and on the passenger side. These were also 4x6's so I bought the right size this time. I bought two Polk Audio 4x6's. So no playing around and cutting for me! I basically just plugged and played on the last two. Im gonna be investing in one more 8' sub and an amp to power my speakers. The Pioneer speakers can handle 300 watts peak power and the Polk's handle just 120. One thing to consider when redoing your audio is that if you have the right tools and the time and patience to do it. One last thing is when ever putting new speakers in solder! Solder solder solder! This will make the sound quality 100x's better.