converting theme to child theme

Hi, is it possible to convert a theme into a child theme and upload a new updated version of the original theme as a parent theme? I’m using a theme that was modified to support my needs and as a result have not been updating it to avoid losing the customizations. Now I discovered a child theme would have been the answer at the time. Would it work if I rename the current theme child and upload the most recent version of the original theme into a new directory? Is it a straightforward thing?
Thanks.