I bought a 2013 Hyundai Elantra and I love this car! However, the heater (not the seat heater) takes a long time to really warm up and never gets super hot. Also, the AC doesn't get very cold. So I want to upgrade these to a better performing (better than what came with this car). What parts do I need to buy for this?

 

Because of the car being so new, you're not really going to find anything that you can replace the heater and AC with. My recommendation is to take it back to the dealer and have them check it. It should still be under warranty since it's so new and if they find there's an issue...it'll be replaced at no charge under warranty.