Your apache config for this site should have something that looks like this:
<VirtualHost *:80>
# The primary domain for this host
ServerName example1.com
# Optionally have other subdomains also managed by this Virtual Host
ServerAlias example1.com *.example1.com
DocumentRoot /var/www/html/example1.com/public_html
<Directory /var/www/html/example1.com/public_html>
Require all granted
# Allow local .htaccess to override Apache configuration settings
AllowOverride all
</Directory>
</VirtualHost>
To change the port Apache is listening to, modify the *:80
to the port of your choice.
To change the ports open to the public, you may need to change the configuration for your firewall other systems.
Here’s a decent tutorial related to getting WordPress set up correctly: https://www.linode.com/docs/websites/cms/configure-apache-to-run-multiple-wordpress-sites-on-one-linode/