How to clean my glofish tank?

I am new to this fish thing. I have a Marina Cool 7 Goldfish Aquarium Kit and 3 Glofish with a filter. I have had them for 2 weeks and I'm freaking out because I have no idea how to clean it. I put those chemicals in it that the lady at petsmart told me to use. But the tank stinks really bad. Please help!