When you say nothing happens do you mean it wont let you change the value or it does but "nothing happens".

Do you run back to the start of the timeframe before playing the scene (as effects dont sometimes take effect untill you start playback, also you need to have "play every frame" set in the settings as this messes up dynamic simulations. also if youve got a chash of particles delete them as this might be the problem.

Other than that you could try extreemes of values as the solver might have changed from when the tutorial was made?

If you still have probs post a pic.

Cheers