Updating to Pro Version

Sakin, I am updating our existing Catch Everest Free version to Pro version. My client provided the downloaded zip file to me, however I have a question. I studied the instructions for installation, however I am not confident in the upgrade steps I should use for my specific situation. I have already created a child theme and the site is already published on the free version. What is the easiest way to upgrade to pro since my site is developed and not new? What should I do to update the parent theme from free to pro and keep my child theme. Todd