When and how should I clean my betta fishes tank?

I recently bought a betta fish last week and he is in his tank. I plan on cleaning it tomorrow but idk how many times or how I should clean it. The tank is 1.2 gallons and it has a filter and a light which keeps the water warm and works as a heater. The tank I have is the national geographic half moon oasis started tank http://m.petsmart.com/h5/hub?id=htt...rter-kit-zid36-21383/cat-36-catid-300065?null this tank comes with a filter and I know the tank is way to small but it's all I can afford now and I plan on buying a five gallon tank soon. Anyhow back to the question. I also have to gravel or rocks but a fake plant and a rock thing in the tank because I lost my bag NO gravel somewhere and have to find it. I have a water conditioner and I use top fin which I found out is really bad quality so I will buy a better quality conditioner after I use this one up. Thanks.