How to edit add-ons?
For adding or editing add-ons, please follow the following steps.
Step 1 - Go to settings from the top navigation bar.
Step 2 - Select the Subscription and Billing settings option.
Step 4: Click on the Upgrade Plan button.
Step 5: Choose your plan. If you want to change billing from monthly to annually you can click on the "Bill annually" option.
Step 6: You can edit the users and add-ons as per your requirements.
Step 7: Click on the Review button. 
Step 8: The details about your subscription will be displayed and you can proceed to checkout.
Note: $7 USD is charged for every 50 GB of additional storage and $7 USD for every 1000 email storage additions.
Step 9: Add your Billing Address and fill in the mandatory fields.
Step 10: Choose your preferred payment method and proceed with the payment.