What seems to be a straightforward operation has me a little confused.

How do I push my updated changes to a custom theme to my wordpress instance?

I.e., I create a custom theme > upload it to my wordpress site > make changes to the same theme in my local environment and update version in style.css.

From here, how do I get wordpress to register the updated version? I tried reuploading the new archive file, but it comes through as a new theme in the admin panel. Seems wonky to me. What's the cleanest way to do this?