If you have a child theme active, you can easily upgrade to Community Builder Pro theme without loosing any customizations.

Steps:-

• Install Community Builder Pro theme by following this guide (do no activate it or install the pro child theme).
• Once you have the theme installed, You will need to edit the “style.css” in your child theme.
• Open your child theme using a file editor.
• Look for a line at the top that says Template: community-builder
• Change it to Template: community-builder-pro
• Save.
• That’s it. You have upgraded successfully.