A rig can really only be scaled if the rigger has made it scaleable. This is because you have to take the scaling into consideration when making the characters limbs squash and stretch. Which can lead to slower, more complex, rig. Not really great for animating. 
It doesn't look like the rigger has included scaling functionallity into this rig.
But when rigs do have scaling it's usually placed somewhere around here on the base control object. (red line marks the place) Either via a special attribute or by having the scaling attributes be unlocked.
I suppose you could learn the ins and outs of rigging and install the functionallity yourself... but at that point you're probably better off just creating a completely new rig from scratch instead of trying to graft stuff onto this one.
Hope this helps.
