In order to upload your presentation you need a CERN indico account (which is not the same as registering to this workshop). In case you do not have the CERN indico account create one as follow:
1) Create a new account here: https://auth.cern.ch/
> Guest access
> New user? Register
2) Once the account is created, you need to login once in indico.cern.ch
then you will have a folder as speaker in "My conference".
When you have the indico CERN account, to upload/delete your presentation look at the following link:
How to upload your presentation
If following these steps you still have problem please contact: