You can delete the Slingbox SOLO from your account by going to accounts.slingbox.com after logging into the website. You can also delete the Slingbox through the Directory that appears after connecting to your working unit on newwatch.slingbox.com. Below is a link that will show you how to use the directory on newwatch.slingbox.com:
Hope this has answered your question!
Sling Media Moderation Team