The theme is not automatically notifying me when an update is available. So when I try to update the Clean Retina Pro theme to the latest version, it says:
‘Installing the theme…
Yes you can use the latest version as you have a active subscription.
And Sorry automatic update feature is not available for now but we will soon add this feature. For now you have to manually install the theme as you did before. Just activate any other theme first and delete the previous version of the Clean Retina Pro theme then upload a latest version of the theme and activate it.
If you have customised a theme without creating a child theme then yes your customized code will be lost. So only customize after creating a Child theme.