In early July at its Worldwide Partner Conference, Microsoft announced plans to make it possible for IT users to upgrade their Office 365 plans more quickly and easily. On August 1, officials shared specifics about that capability via a post on the "Office 365 Technology" blog.
Users can switch to more feature-rich plans (but seemingly cannot back track to less-costly/powerful ones) by clicking on the Switch Plans link on the Office 365 admin center. Once admins select and purchase new plans, their users will be automatically reassigned to the plans' new subscriptions. Customers will receive credits for the unusued portions of their previous subscriptions.
Not all plans can benefit from this automatic switching, but Microsoft is commiting to expand the switching capability "in the future," according to the blog post. Also: Only those with plans covering 300 users or fewer can use the automatic switching wizard at this time.
Here's a list of the plans which are supported currently as part of the new switching option:
Read more at: Microsoft details new Office 365 upgrade options | ZDNet