In order to upload your talk, first login. Then you will see in the menu on the left My conference |_ My contributions. Click on My contributions. Your contributions should appear. Then choose View in the one that you want (in case you have more than one), then on the right click on Edit material. A window will appear, click on Add material and then Choose the file that you want to add. On the same window you could delete previously uploaded materiall that you want to correct.
Please upload your talk in pdf format, well in advance of the start of your session.