Unfortunately if you do not remember the Slingbox password (Administrator password), the only way to reset this password is to hard reset the Slingbox and set back up again.
If you do not know how to reset your Slingbox, have a look at the following article:
Remember after resetting your Slingbox, you will have to go to setup on slingbox.com to setup your unit again. This is required from a Windows computer or a Mac computer. Mobile phones or tablets will not allow the setup.
Hope this helps!!
Sling Media Moderation Team