If all of your Ads settings are greyed out, and you see this message at the top of your Ads settings page:

Please reach out to us through the chat widget on this page, and we'll be happy to help. 

If only your Above placement setting is greyed out (and you can still add in-thread and bottom placements), you'll want to purchase an Ads-free subscription to remove ads from the Above placement. More information on subscribing to an Ads-free plan may be found here: https://help.disqus.com/en/articles/1717307-subscription-payments-faq