I'm not sure about calling the low C on a Treble clef C1, but C5 is the split pint between the Bass and Treble. You can change this, but only for the staff view that contains the treble and bass clef at the same time. In staff view
Edit > layout
Clef > Treble/bass
Edit the spit point.
Alternatively, you can transpose the Midi Track, so the track sounds a different octave. It will still ca it the same in piano roll, but it will sound higher or lower.
Track Inspector
Key+ (Scroll your mouse wheel for semitones, or hold the CTRL key at the same time for octaves)