Hi Jon,
Currently, the Exchange Online Plan 1 belongs to Office 365 for Enterprises (according to Select an Office 365 plan for business), therefore, we cannot directly move it to the Office 365 Small Business Premium because they do not in the same service family.
For detailed information, you may refer to Can I change my Office 365 plan or subscription.
If you have any other concerns about subscriptions or billings, I suggest you contact our sales & billing team by referring to Contact support for technical, presales, billing, and subscription issues.
Thanks,
Allen Zhang