With your first degree (no matter in what subject) you pretty much qualify to apply to the faculties of law at Legon or KNUST.
You are quite a few steps from becoming a corporate lawyer:
1. Get into a law degree programme.
2. Choose electives (at the right time) with a focus on business law. Such electives include Commercial Law and International Trade & Investment Law.
3. Get into the Ghana School of Law after graduating with a law degree.
4. Graduate from law school and gain admission to the bar (become a lawyer).
5. Gain admission into a law firm which focuses on corporate law.