Looking for Changed Files Only

If you have made changes to the core files, you would have to reitroduce those changes in every new install of WP.
Chanses are good however, that you have only made changes to files within your wp-content directory, for example to your theme.

If that’s the case, don’t worry. You don’t have to overwrite anything in the wp-content directory.
When you copy the new distribution over the old, just leave out the wp-content, and keep your old.

Check this thread:
https://www.ads-software.com/support/topic/64309?replies=22

Amazing P!