This is only thing I found. You can change the side bolsters but the don't call it bolsters. In the owners manual it says:
Backrest width
Change the width of the backrest
using the side wings to adjust
the lateral support.
So I am ASSuming that they are talking about the side bolsters(wings) when they say that. I tried to get a copy of it but wouldn't let me. The control is above the lumbar support (round control)chrisny has a picture of it above.
I'll find out more Thursday when I pick mine up!!