Upgrading theme over an existing install

What are the easiest procedures to upgrade a theme in a site that was already developed using the older version

What you mean is to update the theme that has been already modified personally, there’s no easy way. You need to go over with the modifications one by one but if you’re interested in, I could create a child theme with the changes from the old version of the theme. Next time, you could just update the current theme and keep using the modified features

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