What you are looking for is not colder air what you want is de humidification. You remove the water from the air 78-80 will feel cold. Check your temperature drop across the indoor coil. This is done by testing the air in the duct 3 ft. up and down stream of the coil. check the drain on the coil when it is running, is it ‘making water’. Your blower speed may be too high if you don’t know how to do this you will need a qualified technician. It should cost you approx $80 or so to have ‘tuneup’ done.

These guys know their AC stuff. You’ll probably have to look elsewhere for keeping things cooler. Maybe an attic fan, cieling fans, or better insulation would help. Planting some trees to shade your house from the sun might be worthwhile too.

Added to the previous answer, I’d suggest ensuring that the unit, particularly the condensor, is not in direct sunlight, nor crowded by plants that might block free airflow.

You only need to replace the refrigerant if it has been leaking out.

If this is not a new unit you should check the filter to make sure it is clean so the airflow is not restricted. You might also need to hose out the radiator fins that dissipate the heat. When they are dirty they seriously reduce the unit’s ability to cool.

The role of the Freon is to draw the heat from the air to the radiator fins where it dissipates and cools. It doesn’t have to be new to work well, you just have to make sure the full amount is there and not leaking away.