I don't know how you do it in your 3D program but in mine I highlight everything and then group it together, if you have more than one object in your model (if you don't group it everthing will scale seperatly and make the item look very odd). You should have a scale button somewhere, just choose this and then drag uniformly (x,y,z) and then when you export it should be scaled.
I found this on the Web:
http://www.wings3d.com/?page_id=923. Hope it helps.
Edit:
I just downloaded Wings3D and had a look at the scaling. It looks like you change to body selection mode and highlight everything, then right click select Scale Uniform and then just drag your mouse until you have the scale you want. Export out and voila.
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