I like to thank everyone for their response, greatly appreciated but unfortunately, because of newer versions of PS I was unable to follow along with the recommended tutorials. I use an old version (CS3)
What I like to do is, use a brush and paint over the brighter sky (top layer) to reveal the darker sky (bottom layer)without affecting the trees and leaves of the top layer (brighter layer) I am familiar with using layer mask to conceal/reveal different parts of each layer but unsure how to use the channels to create the selection around the trees.
Hope this is enough information
Thank you for your time