How to mute phone ringing??

Hi all,

For the life of me i cannot figure this out. When my phone rings i want to be able to mute the vibrate/ringtone.

On my 9900 i could press the top button and it would mute everything, whereas on my z10 ive tried pressing the top button when my phone rings but it keeps ringing.

So is this possible on the Z10?? if so how??

Thanks