Borge on "Subdomain to main domain - easiest way?"

A client took it upon themselves to try to redesign their website and created a subdomain to create it. Now they want me to move it to the main domain.

Should I move all of the files over? Or should I do a redirect?

What is the easiest way to handle this?? TIA

Follow this guide: https://codex.wordpress.org/Moving_WordPress#Changing_Your_Domain_Name_and_URLs

I was able to move to the new domain. But now all of my pages are throwing 404 errors. I think it might be my .htaccess file?

Try re-saving your permalink structure at Settings/Permalinks in your admin panel. If WordPress cannot automatically edit the .htaccess file, it will provide manual instructions after saving.

.htaccess will do as if it was installed from a subdomain RewriteBase will be changed. So you need to take it back to

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress