Tektro Spyre C — is the rotor riveted to the hub? I recently bought the Cube Nuroad FE. I features Tektro Spyre C mechanical disk brakes, and I am underwhelmed by their stopping performance, especially on the rear wheel. I am thinking about changing the rotor and the pads, however after inspecting the bike it seems the rotor is not screwed to the hub but actually is riveted to it.

Can somebody confirm this?
Rotors are wear items and therefore must be removable. 

The Cube website does not specify what rotors are fitted, but I strongly suspect they are Shimano Center-lock which have a steel rotor riveted to an alloy ‘spider’.  They are fixed to the hub with a central lock ring. 

Changing the rotor will not improve braking performance, unless you are thinking of replacing it with a bigger one.