Once you're logged in to the CMS, go to My Commonspot (or switch to edit view on any page in your subsite) and click on "My Content"
From the drop down menu, pick "My Pages..."
Find the document you want to update and click on the little pencil icon to the right.
From the drop down menu, click "Upload New Version..."
In the new window that opens, click "Browse" and then choose the new document from your computer.
Then click "Finish."
Confirm that your pdf is updated.
Tulane University, New Orleans, LA 70118 504-865-5000 firstname.lastname@example.org