Changing the audio tempo

Hi there, could anyone explain to me how to change the tempo for the whole audio tracks in the project with cubase 6? I watch one the video in you tube looks very simple and easy to do it but when i tried it just messed up. Please help thanks.

Golddie

Does your Bars/Beats grid follow the track?

Hi Grim, i got it now, in pool media i have to changed the tempo for all track should be the same, mark to musical mode and then pick elastic pro done!, you can playing arround with the tempo now. Yes the bars/beat following the track. Thanks.

Golddie