You should make sure that your Facebook account is secure as its your digital identity. If you have any doubt about your account’s security, or if you feel that it has been compromised, then you should immediately change your Facebook password. Here’s the procedure,
How To Change Your Facebook Password
1. Login to your Facebook account, and go to Account > Account Settings. The Account link is available on the top right corner of the Facebook interface.
2. On the Account Settings page, click on the change link next to the Password field.
3. This will open the password reset form where you can change your Facebook Password.
Remember that once you change your Facebook password, you will be automatically logged out from all the other devices.