The refrigerant does not go bad and does not need to be "changed"
If it's leaking, the system needs to be fixed.
It is normal for the AC to blow warmer when outside temps are higher, but no, it should not be "hot".
You can try topping it up with a DIY kit, but that's really just a temporary fix, and quite often the stop-leak in the DIY kits will fuck up the compressor when the system is finally opened up for a proper repair.
IF you go DIY, resist the urge to overcharge. Everyone seems to think that more "freon" means it will work better... this is not the case.
You may already be overcharged if someone has done the DIY thing already.
When it it hotter, the pressure in the system goes up.
The system has a low-pressure sensor to protect the compressor from being run with insufficient refrigerant, but there is also a high-limit sensor that shuts the compressor down when system pressure gets too high.
Tomorrow, open the hood and watch the compressor. When you turn the AC on, the clutch should engage. If it does not engage, then wait until tomorrow night after it cools down, and verify that it engages then. If so, the system is overcharged and needs to be properly balanced.
Seriously... the best thing to do is take it to a shop and have the system checked.