No air flow upstairs

Question

I live in a townhouse and the downstairs is nice and cool when running the air, however, the upstairs is HOT. There is no airflow coming up the vents.....I read that you can turn off the downstairs vents, but they are on the ceiling (look like smoke alarms).I don't know what to do! Very uncomfortable upstairs.The pipes are cold, and I can feel the cold air downstairs, so I don't think its the unit itself, just no flow going up the vents.