Replace existing live wordpress site with new one built locally w MAMP

I have an existing live wordpress site at my purchased domain and I host it through godaddy.

I’ve also recently built a brand new site locally using MAMP. I downloaded a theme and created a child theme to customize the look how I like. I’ve set up login creds and a new database through the MAMP myPHPadmin. I want this to be my new site.

How do I swap the existing wordpress-built site that is live now with the new site I built locally? I have FileZilla as my FTP client and have my hosting credentials for the current site.

I made the mistake of simply trying to replace the existing “wp-content” file with the new one using FileZilla and it did not work other than, from what I can tell, merging the two into one ugly site! I feel there is a step I am missing. Can someone please clarify?

This is my first attempt to try and change my website. Did I not replace the right files? Is there a step I am missing?

Again these are both wordpress file structures, both existing and the one I built locally. Apologies if this has been answered but I could not find what I needed searching the forums. Thanks!