I understand that you are having some issues in order to update the software through www.slingbox.com on your Mac computer.
Most of the times, this issue might be related to the Operating System or web browser versions in use. With this in mind, I recommend you to check the following link:
Once you've checked this link and updated the available versions (if necessary) I encourage you to check this article and follow the detailed instructions:
If the issue persists, I encourage you to contact us in order to help you out.
Hope this helps!