You're using the wrong tool.
Process > Transpose is, as far as I'm aware, for Midi notes only (where it works perfectly incidentally)
What you need is a pitch shifter, but be advised that most of them are only good for shifting in small increments before it introduces nasty artifacts.
There is one included under Cakewalk Fx, give it a try. If the results are hopeless then you'll have to look at a 3rd party solution