1.) You will need to transfer all your custom templates files and custom codes in your X child theme's functions.php file to your Pro child theme. If you are unsure, then it is better to convert your X child theme into a Pro Child theme instead. Simply go to Appearance > Editor. Edit your X child theme's style.css and make sure it starts with like this:
Theme Name: X – Child Theme
Theme URI: http://theme.co/x/
Author URI: http://theme.co/
Description: Make all of your modifications to X in this child theme.
What has changed? The template name which is originally
x were change to
pro so that the parent theme will not be Pro theme.
2.) It is no longer necessary to activate Pro child theme if you opted to edit your X child theme's style.css. If you did not, then you will need to activate it.
If you have installed a caching plugin, please go to the plugin's settings and find the "Clear Cache" or "Delete Cache" link or button. For your browser cache, you can check out this guide:
Hope this helps.