Throw away all of your existing speakers, and buy the best 13cm components (mid, tweeter and cross-over) you can afford. Fit the mids in the standard door locations, and tweeters in the dash positions.
As you've spent all of your money on the above components, you're now gonna have to mug somebody to get the money to buy a suitable amp to power them. 4x40 from a head unit is PEAK power - more like 4x8 if you're lucky. A good 2 channel amp putting out 2x40watts RMS should do the trick.
If this sounds like too much - get some good modern 13cm co-axials for the doors, and amp them if you want some decent oomph. Depends how much you want to spend.