On the left navigation menu, under "Company Profile".

Click on "Certifications" to go to the certifications section, which displays the list of the certifications you have in your profile.

To add a new certification or edit an existing certification, click on the "Edit" button. It will open up an edit pane on the right. 

Add new certification, click "Add More Certifications"

To edit a certification, click "Remove" next to the certification and then click "Add More Certifications" to add it as a new certification.