In case a subscription needs to be cancelled, please downgrade the amount of licenses to one license first. It is not possible to downgrade to zero licenses.
Then please continue with this article: How to cancel and destroy a Subscription.
Upgrading can either be done via ‘Office365’ → Licenses → choose the desired subscription → 'Buy More',
or via “Account” → Subscriptions → choose the desired subscription → Change Resource Limits.
Downgrading is not possible from the 'Buy More' button. You can downgrade and upgrade from the 'Subscriptions' setting.
When you need to upgrade or downgrade a number of resources such as licenses or add-ons you can always use the same procedure for all products. In short: Go to ‘Account' > ‘Subscriptions’ > Click the subscription > Click 'Change resource limits’
Go to 'Account' > 'Subscriptions'
Click on the subscription for which you want to add or remove resources
Click 'Change Resource Limits'
Select the number of resources you require followed by 'Ok'
The order will now be placed.