How to switch my primary domain name with my add-on domain?

Here are the steps you should take in order to switch the two domains, i.e. make yourdomain2.com primary for your account and host yourdomain1.com as an addon domain:

Remove addon domain from the addon slot from your cPanel > Addon domains.

Change the primary domain name for your account from currentname  to addondomain name. This can be done from  Help Desk > Domain name change.

Back up the website files for primary domain located in the public_html folder and then  place them in another folder.

Move the files from the addon domain’s folder to your public_html directory.

Add primary domain to your addon slot from your cPanel > Addon domains.

Copy/restore the website files for primary domain to the newly created addon folder.