For adding an existing domain to your WordPress.Com blog. Follow these steps:
Step 1. Update your domain’s name servers to following:
- NS1.WORDPRESS.COM
- NS2.WORDPRESS.COM
- NS3.WORDPRESS.COM
Step 2. Wait for the name server changes take effect. And then visit Dashboard -> Store -> Domains.
Step 3. Enter your domain name in the box and click ‘Add domain to blog’ button.
Step 4. When the servers are verified, it will prompt you to pay for the upgrade and complete the process.
Step 5. After purchase visit Dashboard -> Settings -> Domains page and click the Update Primary Domain button.