You can access course certificates by going to 'My Courses' and then clicking "VIEW" next to the course name. The course info will pop up and the 'Certificate' link will appear under the course name. Please note that you must first provide course feedback and pass the exam to access your certificate.
The certificate should download as a PDF to your computer, so make sure you have a PDF reader installed. If it doesn't download immediately, try downloading it from a different internet browser to see if that does the trick!