Hi

I am confused as to why you cannot change aperture. since I am on a slighty different course (The diploma in Photography) I am not 100% sure about the module

but if you are meant to be using 'P' mode, the camera ought to allow you to switch through various options for correct exposure any way.

e.g. 1/125 and f8, 1/60 and f11 or 1/500 and f5.6.

What does the course book want you do for this section?

Also, many full frame lenses have no aperture ring, lack of an aperture ring is not an indicator of being a lens for a DSLR.