register more than one person using shopping cart

Hi guys

I currently have shopping cart set up, and most of our events are book the member only.
So when a member books an event they cannot modify their shopping cart to more than 'quantity' '1'

How can I set it so, that for a single event, they can increase the 'quantity' in the cart to more than '1'



I am sure there is just something I have set that I need to change, but i cannot figure it out.

Thanks
Alison