To recover your hacked Gmail account, follow the steps in this article. Here is also a help page that explains how to recover and secure your Gmail account when it is hacked.
EDIT: I noticed that you have posted your question on the Facebook forum. If your Facebook account is hacked, see this answer.
You can change the password as per your account recovery details filled. If you are not able to recover the account then you can raise your issue in the help section and the support team will revert to you with the solution asap.