The crown pad and cheek pads are removable in most Arai helmets, this is so the helmet can be custom fitted to your head.
Changing a helmet from one size to another, for example changing a medium shell to fit like a large, depends on the helmet itself. Please note you can only change between sizes where the shell size is the same.
See attached PDF file for helmet conversion tables. If you have any trouble contact us or your local Arai DNA centre