A few week ago, just before Christmas (2013). Microsoft added a new feature to Office 365. So that we can now change our Office 365 plan or subscription. This was actually announced back in August.
This is great news, since before this, if we bought a Small Business or Medium Business Plan, we were locked to this Plan. Now we can “upgrade” the Plan to e.g. Enterprise Plan is needed and thereby easier grow within our Office 365 tenant.
Supported upgrade scenarios
Certain upgrade scenarios are supported. Mainly it’s from a lower plan to a larger, more feature rich plan. See all the scenarios at: Switch to a different Office 365 plan or subscription.
All information on how to switch and what scenario is supported, is listed in the Office 365 help page: Switch to a different Office 365 plan or subscription.
Reference: TechNet blog post.