Injectors

Hey do injectors increase power? and if so what would be the best for my 99' 3.8L firebird

Injectors don't make more power the fuel they inject into the combustion chamber makes more power. You can increase the amount of power you get by changing the injectors to ones that flow more fuel at a higher pressure. A stock non-modified engine, can't handle all this fuel however and you should only consider changing if you intend to modify the engine to a higher compression with a higher lift cam and a larger throttle body.

So how do i change my engine to a higher compression? and what would you recommend for a cam and a throttle body?

Either replace your heads or have the current ones machined. Replace the pistons.