Step 1. Back up the site you wish to overwrite
Because you already have a live site present, it’s good practice to back up the the existing site before installing a new one over it. Install the Duplicator Pro plugin on the destination site and create a package. Using one of the cloud storage options is the best option to keep it safe.
Step 2. Install an HTML maintenance page (optional)
Depending on your situation and traffic, you’ll usually want to avoid having visitors experience HTTP errors while your site is being restored. To address this, download an HTML maintenance page and name it ‘index.html’ so anyone who hits your site will be know it’s under maintenance.
This page has a list of free and commercial maintenance pages you can use. Important: These are HTML pages and not WordPress plugins. This is important since you’ll be replacing the existing site thus installing a WordPress plugin isn’t appropriate for this scenario.
Step 3. Put the installer.php and archive files in the site’s directory
Just as is done with a standard install, put the installer and archive files in the directory where you wish to install the site.
Step 4. Browse to the Installer
At this point, start the installation by browsing to the installer.php file. You’ll notice that the “Mode” indication in the upper right-hand corner of the installer will show “Overwrite Install” in red.
Continue with the install. On step 2 you will be notified that an existing wp-config.php has been detected and it will ask you if you want to use the database credentials found in that file.
Click the “Apply” button to reuse the credentials and then continue with the install.
After everything is done the site that had been contained in the package will have been installed on top of the existing site.
Step 5. Remove the maintenance page and you’re done
Now that the site has been installed you may now delete the maintenance page installed in step 2.
And that’s it – the previous site is gone and the backup has been restored.
Wait! Something doesn’t look right!
In the event that something has gone wrong or doesn’t look right you have the option of either attempting to correct it or restore the site that was in place before you installed.
To restore the old site, simply copy the installer and archive files that you created in step 1 to the website’s directory and install.