Convert the model to an STL and then grab a copy of the free Netfabb Basic.
It has a tool to change the scale of the model.Patience, Persistance, Politeness - the 3Ps will help us get us to Perfect Printed Products
Netfab basic can open OBJ.
So you should be able to do as stony said with your obj. You could also scale it up by 10 in the software you created it in, then when you upload as mm it should be the correct size. Your friendly neighborhood Moderman