Switching from Subdirectory to Subdomain (Don't thin I'm using Multisite?)

I have a website, and I’m just hearing about multisite, I don’t know if I’m using it (Something you have to enable? chcked wp.config nothing is there about it)

I want to switch from my subdirectory
http://www.example.com/hello to-> hello.example.com

Is there a simple way to do this? I thought of just downloading the directory, deleting the old directory, creating the new subdomain, and adding those downloaded files to the subdomain, then using a plugin to redirect anything that’s broken, would that work? or are there other ways to do it?