Get the AC checked by a Pro to make sure it has clean coils and enough freon etc. Also get him to check the airflow thru the vents in the house and see if some can be closed partly to force more air upstairs. Don't start doing that yourself because you may restrict the airflow too much and freezeup the furnace coil and damage the compressor. The tech can see if closing the vents causes a problem and make sure it is working properly.