How do I get my product.templates and collection.templates in my updated premium theme?

[Bramm]

After logging in this morning I saw that the people at Clean Canvas had another theme "update" available. 

"Your code changes won't be included because one or more changes conflict with the update. After the updated theme is added to your theme library, you will be able to copy your code over or re-configure some apps."

After checking the updated version in preview mode I noticed that basically all of the modifications dissapeared and to be quite honest it looked like a mess. I then copy/pasted the theme.liquid and styles from the working theme code and things were looking okay again. Unfortunately the updated version doesn't include any of my collection/product templates so I wanted to know if there is a way to copy them from the working theme into the updated version. I hope I don't have to manually add them one by one because this will take me hours. 

I have contacted Clean Canvas in the past but the only help they offer is one of their partners who would charge me for it. 

Appreciate the help!

[PaulNewton]

Export the old theme and new theme, download to local desktop, create backups.

Unzip the zipped theme exports open folders for both. 

Copy files from old to new, zip, upload, test.

Repeat if broken.

Beyond that if you have heavily customized theme you should be using either shopify's theme kit or the shopify-cli to aid managing theme.

Preferably also with either local version control, or using shopify's github integration

https://shopify.dev/themes/tools/theme-kit 

https://shopify.dev/themes/tools/cli/ 

https://shopify.dev/themes/tools/github/