ANSYS: Change Material

I am setting up a simulation in ANSYS Workbench 

I have input the geometry from ProE. There are two peices. One is aluminium (rolled and polished), the other is titanium.

I know and understand how to change material properties.

However, both of the peices have been set as aluminium; I didnt set this, it must have been a default setting.

How do I change the titanium peice from aluminium to titanium? What option do I select? In what stage? Geometry, mesh, pre?

Thanks a lot!