Does that bike have SORA shifter? Combo Brake lever shifter? I have an older version. Mine has a little trigger to shift to higher gears, very easy. To shift back to lower gears, you push the brake lever inwards. Sometimes when it is cold, that part balks a bit and doesn't shift, I am thinking the cold thickens up the lube and the little bits don't click smoothly. Might just need cleaning and new lube.