Please follow these steps:
Menu in the upper left corner of the App - My Account - My Packages - Click the "Upgrade" button behind the current package - Enter the upgrade package interface:
Select the new plan you want to upgrade to or the number of devices you want to increase under "New Plan" below.
If you only want to add more devices to the original package, please select your current package type in the new package and then add the number of devices below.