The most common reason for a home AC unit to not be cooling is dirty air filters. Your air filter traps pollutants in the air before it enters the air conditioning system. However, over time, this causes your filter to get dirty and blocked. A dirty filter can severely reduce the cooling capacity of your air conditioner if it isn't changed regularly.
Your condenser might also be the cause. Your condenser needs lots of breathing room. Otherwise, all of the heat you've gathered will be blown straight back into your home, making it hard for the AC to cool down below 80 degrees. Check the area around your condenser for any shrubs, fences or debris that might be obstructing the breathing space of your condenser.