First of all, I would advice you to try and figure out how someone could gain access to your account.
Secure the leak instantly, else regaining your account will only be a short time solution.

After you have restored the security, please consult this article: I've forgotten my password. Or, I've been hacked. How do I get my key back?

As a side note, please make sure that you post in the correct forum. That helps people who search the forum to find a similar topic faster.