Changing a package for any cPanel user is very simple and can be done on the WHM panel.
Log in to WHM panel;
Choose the button “Account Functions” on the main menu;
In the next menu choose “Upgrade/Downgrade an account” button;
Choose a user from the list and press “Modify”;
You will be able to see the package list and choose a new one. Then press “Upgrade/Downgrade” button.
The package is changed immediately.