The default GPU is the Intel one as it uses less battery power and you don't need the more powerful AMD GPU just to run Windows or to run general applications, that would just waste battery power with no advantages at all.
Your laptop will automatically switch to the AMD Radeon one when you run an application or a game which requires more a powerful graphics engine, but the battery won't last as long between charges when that GPU is used.
You should also be able to manually assign the AMD Radeon GPU to a particular application or game using the Catalyst Control Centre in Control Panel.