If you ever feel unsecure about loosing your password or you think that you're hacked, in this case you need to change your password in order to do that go first log in to your facebook account with the old e-mail and password:
1 the gear button and select Account Settings.
2 Look for the password line and click Edit to the far right.
3 Enter your new password and re-write it again then click Save Changes.
Now your password has been changed successfully and if you forget to log in with new password next time, you'll be reminded that you've changed your password at a certain time.