I am new to hosting and migrating websites, maybe someone can help me. I've got an zip-folder which contains a .daf file and an installer.php file. I should update the functionality and design of the old website while maintaining the content of the current website. Whats best practice to do so? Trying to understand this, I already learned that the files are generated by the duplicator plugin and running the installer file on my webspace would delete all my content and just show the new site, which would remove all my posts and so on. I tried to extract the .daf file to just get the theme, but trying to load the .zip file of the extracted theme resulted in a more or less blank page (I guess because of missing plugins and files the theme uses).

So should i export my posts, run the installer.php on the webspace on a subdomain and then check if everything works after reimporting the posts or is there a better way of doing this. Maybe the duplicator plugin itself helps with this problem. Thanks for any input :)