You are absolutely wrong place.
You already buy a domain name and created a wordpress.com blog!
This is wordpress.org (self hosted WordPress) support forum. Read this article to understand the difference between them.
If you want to install a self hosted WordPress, you need a host that support PHP, database etc.
The cPanel is a fecility by hosting providers to manage our assets, not from domain name registrars.
Else you can use your wordpress.com blog with your domain. But you want to upgrade your wordpress.com blog, ie you want to pay for it.
So before any further action, you need to learn more. Else you will lost your money and time.