Basic car performance questions

[Crapozo]

Hello,

I just recently found a flash game on the internet called Drag Racer Version 3, and i find it quite interesting.

Anyway from playing the game i have found out a few things about manual cars which i have a few questions on:

1. You can change the gear setup (speed) with cars to give em more horsepower, torque etc...
How do you do this? I think for the newer cars you can do it digitally but how about older cars?

2. When you approach the red section of the RPM meter the temperature goes up dramatically. But what is it the actual temperature of? The petrol?

3.If the temperature goes too high, the car engine gets "blown". So what would this mean, in real life i would have to replace the entire engine? What is actually blown?

4.And is it possible to tune a automatic transmission too?