If you really want it permanently straightened, you can use a chemical relaxer, or use a texturizer (a mild application of a chemical relaxer) to loosen the curl. You can do that but understand it will probably lead to extra work and extra trouble.
Relaxers/texturizers tend to steal the life from hair, flattening it and robbing it of dimension and movement. It can look artificial. Also, it tends to be dry, even rough. I've used both of these with regret.
Moreover, relaxers sometimes don't work. If your curl pattern is really strong, you may be left with some curl or wave, despite the treatment. For me, there wasn't a relaxer strong enough to keep my hair from curling.
Also, even with a relaxer it often reverts back to its curly state when wet or when you sweat. Which can mean you have to blow dry it straight after wetting it each time or it will dry curly again. This often leads to damage from excessive use of heat.
Flat-ironing hair damages it as much as relaxers do. Fighting Mother Nature comes at a cost.