It depends. It is possible your problem is a lack of insulation in the attic or uninsulated windows. It is also possible that your air conditioner is undersized or the ductwork in your home is undersized. You could also need more return air vents.
If you suspect the issue is with your air conditioner, the first step would be to have a technician come to your home and make sure everything is sized properly, including the air conditioner and the ductwork. They will also check things like the refrigerant levels to make sure they are not too low or too high.
If the problem is with the ductwork, it can be fixed. Many times it is messy and requires a lot of drywall patching and repainting. It may be that the best solution is a new ductless technology called a mini-split system. One of our HVAC supervisors can show you what options are available and the price of each option. This visit is free and there is no obligation to buy a new AC unit.