If you wish to change your password, you'll first need to login to your profile.
1. Click on the menu icon on the top right of the page (to the right of your picture), click on Settings, then Account Settings
2. Under My account settings click change next to Password to update this information.
3. Type in the new password you wish to use. You must type it in again and both passwords must match. You can then click change password when you're done.