How to change Alarm ringtone?

I tried alot but I can't seem to find the way to change the alarm ringtone for my Torch?

What I want to do is I want to set my phone on silent mode when I sleep, yet have a customer ringtone play at a loud volume when the alarm time reaches.

Thanks in advance.

Bedside mode.

start the clock app > BB button > options > scroll down to alarm section.

Then when you want it to take place use the clock app and press the BB button and chose bedside mode.

Thanks alot d00d! Worked so easily :D