You can't directly access iCloud from the iPad. Pretty much all iCloud activity on the iPad is controlled through the apps and/or settings. You need to go to iCloud.com on a computer. Even if you try and fool the site by using a browser on the iPad that pretends to be a desktop browser. Not because it won't try, but because the site won't work.
You can not delete individual pictures form the PhotoStream. That's what I assume you are trying to do. Instead all you can do is reset the entire stream, removing all photos from it.
To do that, once you are logged into iCloud.com, click on your name at the top right of the screen (you won't see if it you have any of the web apps open). A control window will appear. Tap on Advanced and Reset Photo Stream.
I haven't found a way to reset the photo stream from the iPad. It seems to be an oversight on Apples part.