Simple edit. I want to remove the top right hand corner and replace with surrounding sky. I have a minimal level of skill with Photoshop.

You would want to look up the Clone Tool so you can replace that part of the sky with another part.

Check this for instance ...

http://www.ephotozine.com/techniques/viewtechnique.cfm?recid=22

.. and you might also want to make a search here on the forum for Clone Stamp or Clone Tool.

William, welcome to RetouchPRO.
The clone tool will fix that corner in less than a minute. You should also consider using the Shadow / Highlight adjustment to bring out a little more detail in the shadows and boost the saturation a little.
Regards, Murray