To access your settings page you must be logged in. Then, on the upper right corner of the site you'll see your profile picture, your name, a link to your settings page and a link to log out.
Click on the "settings" link to open your settings page. Then choose the option password on the top of the page.
On this page you can change your current password. Just fill in your current password and the new one and click the pink button.
The next time you log in to the site you'll have to use the new password. Your old password will stop working.