Forget working "lower abs" and "upper abs". Just work the abs
Most movements that are supposed to work the "lower abs" really target the hip flexors in your thighs. The musculus rectus abdominis (=abs) is ONE muscle, and it's main function is to hold and move the spine (and keep your bowels in place), not the legs (or hips!)!
So, any exercise targetting this muscle involves a movement of the spine ALONE (or static hold). It's not really important if you roll your hip or your shoulders upward, but shoulders is easier.
Do crunches, crunches and crunches as your main three exercises. Then maybe side crunches, reverse crunches, static holds, leg lifts etc. You don't need a machine to work your abs. Only be sure to do abs after all other exercises that require core stability. It's not a particularly good idea to do squats after 15 minutes of crunches