Please make sure you are "Logged in" (top right corner).
Click on the menu on Contribution List and then click on your presentation title.
Click on the "pencil" next to Presentation Materials.
In Manage Material, select Upload files.
Click on "browse" to look for and upload your presentation and then click on Upload at the bottom of the window.
Please note that you need a Cern external lightweight account or a Cern Nice account to upload your presentation.
If you are not already in possession of one; please register for an external lightweight account through this link.
Once it is done return to your email to confirm this request !
If you already have an account, but there seems to be a problem: please refer to the same link and/or contact the CERN helpdesk + 41 22 767 7777.