One thing you can try first is to add "?f=json" to the end of your URL, this should return the resource's JSON definition. I've encountered a lot of ArcGIS Server sites that forbid HTML viewing but are fine with JSON, you might be in the same boat.
Are you asking because you are an administrator or a user? If you are just a user, or even a publisher, you will not have the privileges to make this type of change. Also, is this stand-alone ArcGIS Server or federated?
