NSA2600 : settings to reduce bandwidth to Youtube

Hello,

We use a Dell SonicWall 2600
Firmware Version: SonicOS Enhanced 6.1.2.0-11n
Safemode Version: SafeMode 6.1.0.9
ROM Version: SonicROM 5.4.0.15.

Some of our users use "a little" too much Youtube but we are not allowed to block it. So, to keep our bandwidth, we want to reduce bandwidth assigned to this website.

The question is : how to proceed ?

I've found a way but for SonicOS 5.5 and all is different with SonicOS6.1.

Do you have any idea ? Don't mind explain a lot, I'm not used with this device.

Thanks a lot