In the future, I hope to add a feature to the site that will allow you to chose the size at which the stencil prints out. But for now, you'll have to get a little crafty.
I'd suggest printing it out at normal size, and then taking it to a copy center (as Niceworkbonedaddy suggested) to have them reduce or enlarge it. Or if you have a scanner, you can scan it into a graphics program and resize it yourself.
Although, I'd be careful about shrinking these designs too much. I try to design them to carve well at the size they originally print. So... depending on the level of detail the pattern has, you may be in for a challenge if you shrink it down too much.