Waqas Butt explores the Dynamics GP 2015 Upgrade Process & Paths.
Microsoft Dynamics ERP’S Blog By Waqas: Dynamics GP 2015 Upgrade Process & Paths
Install, Upgrade & AdminMicrosoft & the GP EcosystemGP 2015
Archived post from 2014. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.