Originally Posted by khuon
I'm assuming you have Sora shifters. When you say upshift, do you mean move to a harder gear or move to an easier gear? Generally speaking, upshifting is moving to a harder gear.
To upshift the rear, you simply push the thumb lever on the side of the right hood.
To upshift the front, you swing the left brake lever inwards towards the centerline of the bike.
To downshift the rear, you swing the right brake lever inwards towards the centerline of the bike.
To downshift the front, you press the thumb lever on the left hood.
These things and more should have been explained to you by the bike shop assuming you purchased the bike from a shop. If you have and they haven't, you may want to return to them and ask them to show you how to operate all the components including shifting, quick releases, brake releases, etc...
an additional thing, which tripped me up test riding a bike, when you are swinging the brake lever inward there will be a small force to overcome and you will hear a click. I rode around trying to get that to shift and stopped pushing when I felt opposing force. So make sure you are pushing hard enough and not just "wiggling" it around paranoid that something is going to break if you push it harder.