Seized Transfer Box

Hi all, ive just become a 1st time disco owner and am already having a problem. Not sure if its me, or something more sinister! After following the instructions for changing from hi to lo ratio on the transfer box, I just cant seam to move the lever. Ive heard that they can seize up if not used. If it is the latter, is it something that can be sorted easily/cheaply or is more likely to be a major expense? Its a 2000(x) td5 auto. Any advice would be appreciated. Thanks

If it's already moved from high to low, it's unlikely to have seized from lack of use, unless something has bent and jammed.
Are you following the instructions to the letter? From memory it should be engine running in neutral. Try blipping the throttle. I know that with the main box in neutral, that shouldn't have any effect, but I have known it help.
If I can remember how to change from low to high on the move in a Td5 Auto, I'll come back, but revs etc were fairly critical, so I won't post that unless I'm sure I've remembered it right.