How Can I Stop Being Shy and Speak Up?

How can I stop being shy and be more present in conversations? I often find myself holding back, either because I overthink what to say or because I don’t want to draw too much attention to myself. I want to be able to express my thoughts confidently, engage more actively in discussions, and stand up for myself when needed. How do I break out of this hesitation and become more assertive without feeling uncomfortable?