Upgrading from free

Hello Forum, I have been using the Catch Everest Free template for some months now and have made customisation's to suit our needs. Some functionality was locked behind the pro version which we wanted so we have purchased the pro version of this template. How do we swap the theme over while keeping all the customisation's we've made to the free template. A step by step process would be greatly appreciated as I haven't been able to find this information on the support website. Thanks.