When I was eight years old I was diagnosed with a speech impediment and the pediatrician recommended that I get speech therapy.
But that's expensive, so I didn't.
Ten years later, I've won a scholarship with a speech and qualified for nationals in a speech-and-debate league.
The thing about speaking is that everyone (and I mean everyone) can improve. Some people are never going to be amazing speakers, and that's okay. But you can get better than you are now.
Some tips that have helped me:
1. One. Word. At. A. Time. It. Sounds. So. Wrong. But. If. You. Force. Yourself. To. Go. Slowly. Then. When. You're. Nervous. And. Speed. Up. You're. Still. At. An. Understandable. Speed.
2. Tricky tumbling tongue-twisters are terrific friends. Say them over and over.
3. Memorize poems, especially those with tricky words. Record yourself reciting them, and listen for what you want to change.
4. Practice, practice, practice. Read out loud to yourself, compose poetry, have long conversations, go ahead and sign up for that speech contest if that's what it takes.