I just got a cheap cessna 747 it came with 2 props a large one and a smaller one which prop should I use for more power and speed?

A Cessna 747????

Generally smaller diameter/larger pitch will give more speed while larger diameter/lower pitch will provide more "pull". It's kind of like the difference between a Corvette in top gear on the open road and a truck in the lowest gear pulling a load up a hill. Both utilize the engine power in different ways to achieve different goals.

yea its a cessna 747 from bananahobby http://www.bananahobby.com/1783.html this things pretty cheap it doesnt have alot of power so i need all the power i can get

Generally draggy designs use larger diameter lower pitch and cleaner designs use smaller diameter, higher pitch. Yours should do better with the smaller diameter larger pitch... but use both and experiement.