When uploading a model, you may see a dialogue box like this indicating that you have a large scale model:
If your model is intended to be larger than 50 meters in length, simply select yes and continue. If your model is not intended to be large-scale, you'll need to select the unit of measure that was used in the program where the model was designed so that it displays correctly in Brio.
This is because Brio's default units are in metres, while some 3D application's default working units (including Maya, Cinema, Modo and a few others) are in centimetres. So, when you import a model from one of these programs, Brio will read its units as in metres and enlarge the model unless you define the correct unit of measure.