http://tiny.cc/mdhfly Secret discount page at Macphun.
I walk through replacing a sky in Luminar, and it's very quick and easy! I use the gradient mask to apply it, the eraser to fix a part of it, and the transform tool to align it perfectly. Then I apply a preset on top of all that, and I have an entirely new image in a couple of minutes. It's easy with Luminar! You can download a free trial copy of Luminar here: http://bit.ly/2hWBNZ5