Rosie,
my best advice that I can give to you is to use anothem program to just edit the mesh you want to
use it, change the surfaces in the sense of regrouping them as one where needed , for example.
I am a Lighwave user, and I found the Modeler of it very fit to it, but I am sure you can find something even free of charge in the net.
For a start, there is the completely free Art of Illusion,
you can find it at

www.artofillusion.org

Follow the step instructions, it requires Java Runtime Enviroonment to run properly (also free stuff...). Of course you have to learn at least the basic of it... but I know that as Bryce user you natively adapt....