A chemical relaxer/texturizer will do it but - as Blueblood indicated - it also compromises the integrity of the hair. And the maintenance? Oy. Or you could hide your hair under a 3a wig. ... Or you could try flat-ironing or hot pressing it, or a Keratin treatment. The Jheri curl is a horrendous, greasy, smelly monstrosity that I shutter to acknowledge at all. All of these take a toll on hair and personally I rarely see drastically straightened hair that looks natural or "healthy". Also, 4c hair is quite fragile as I understand it and can break from all these methods.
One of the simplest, but possibly most challenging remedies is to accept the natural beauty of your hair and learn to embrace it with all you have and for all its worth (which is a lot). I sympathize with you because I recall wanting straight, blond hair when I was a kid when what I really
possess is a naturally strong curl pattern, naturally brown
One place to start is in the 4 forum. There's a lot of knowledge and humor there. There's also plenty of beautiful hair to gawk at, including 4c
You might want to check that out, along with the other forums here.