Can I revoke a power of attorney I previously granted to someone?

Yes, as the person who granted the power of attorney (the principal), you generally retain the right to revoke it at any time, as long as you remain mentally competent to do so — a power of attorney isn't irrevocable simply because it was granted, unless it was specifically created as part of a larger, separate binding arrangement where revocation would breach that other agreement.

To revoke it properly, you should execute a formal deed of revocation, and importantly, notify the attorney (the person you gave the power to) and any third parties who may be relying on the original power of attorney — such as banks, if it was used for financial matters, or the sub-registrar's office, if it was used for property transactions.

Failing to properly notify relevant third parties can create complications, since they may continue to treat the power of attorney as valid until they're formally informed of the revocation. A lawyer can help you properly draft and execute the revocation, and identify who specifically needs to be notified given how the original power of attorney was being used.