1. Before the deadline for application closes, you can upload your supporting documents via the CV under “My account”/”My CV” (do not forget to submit your application as the documents would otherwise not be transferred to your application).
    
2. After the deadline for application closes and before the deadline for submitting supporting documents closes, supporting documents must be uploaded directly to the applications by clicking on the existing entries and attaching the documents via the paperclip (and not to the CV - the data you add to your CV after the applications close will not transfer to your application). 

Instructions can be found at How to apply for a competition - Overview.

For more information please read: Which supporting documents should I provide?