How do formula 1 cars get so much hp from a 2.4l engine

May be...

F1 engines are normally aspirated, which means one can only get so much air into it, less than atmospheric pressure at best.
So you have a certain amount of air, no matter how much fuel you can throw into it without sucking in any more air you're not gonna get lots of power.
That's why F1 engines don't produce lots of torque, around 55 Kgm which is less than your neighbors' turbocharged Audi.
The secret to getting power out of normally aspirated engine is to rev it as high as possible.
You want crazy power you have to rev like crazy and that's what they do.
They are rev limited at 19000rpm or they would already be past 20000 which any way you look at it is nothing short of insane for a big 4 stroke cylinder.

aerodynamics , light weight , formula 1 fuel
and if your an american european engines are usually smaller size but with the same power as american cars because of using cleaner fuel

its the fuel they use (formula 1)

If you supercharge a 4 cylinder 16 valve overhead cam engine with dual 3 in. exhaust and use a high performance ignition 20,000 volts or better, then put it all in a light weight carbon fiber body thats what you get.

Well, without going all geeky and confusing.
An F1 engine only weighs approx 100kg, only has to last 400kms and can rev up to around 19,000 rpm, where most road cars go to about 6000rpm.
Economy is sacrificed, 3.5 mpg tops, no chocking emissions equipment like catalytic converters.

Julian and Christos have given good answers so I'll add just a little bit more.
As they've pointed out, the power comes from the extremely high rev range. The reason they achieve this in such a small engine is reasonably simple actually.
It seems as though a shorter piston stroke allows higher engine speeds to be achieved. So by reducing the length of the stroke the bore size is increased a proportional amount resulting in a 2.4l engine. So, in a normal road car you have a narrow piston with a long stroke and an F1 car just has a really fat piston that doesn't have to travel as far.
That's about as well as my limited mechanical knowledge can explain it unfortunately. I hope this coupled with some of the other answers helps.