Yaris T1 stock speaker upgrade

[CrzyCrg]

Ok, here's probably the most simple question you will get on this forum. I just bought a second hand T1 Yaris... Basically, all I want to do is upgrade the stock speakers... I was thinking Infinity splits up front and I have no clue what to do in the back. It's a 3 door model. All that I really want is a bit more bass and nice clarity without doing a full install. (i.e. amps, sub etc.) Any advice would be greatly appreciated especially tips on taking door panels etc apart. I've installed in golfs, hyundais, fords, but this is the first time on a Toyota!

Thanks!