Click on the logo/name of you company on the menu bar on the top right hand side of the screen.
Click on My Account.
Click the tick-box next to Change Password?.
Now you can type in your old password followed by your new password. And when you have filled it in press "Update" on the bottom of the page.
If you entered your old password in correctly and your new password meets the requirements congratulations you have changed your password. If something was filled out incorrectly then a error message will appear and you might need to make a adjustment to it