Had the models made but the walls are too thin. Help!

I paid someone to design a set of key caps for as I do not have the experience in CAD/ other design software to do so and wanted it done right. I did not originally intend to print with shapeways, but after I submitted my models to shapeways it appears my keycap wall thickness (about 5 mm) Is too thin for shapeways to print.

Are there are easy guides or tutorials on how to fix those in sketch up or any other beginner 3D software? I only need to increase my wall thickness by .2 mm. All I need to do is increase their thickness.

here is my shop with the models. The autofix is not a good solution to use in this case.

https://www.shapeways.com/shops/P3T

I'm guessing you mean the thickness is .5mm? Which model is it that you are talking about?