They're all different levels of difficulty - best bet is to go along and explain to the instructor what your level of fitness is. That way (if they're a good instructor) when they give more challenging moves, they'll explain what to do as an easier alternative. That's what seems to happen at the classes at my gym anyway.
The last LBT class I went to, there were some uber-fit people, normal people, me and some OAPs (including one lady who'd had a knee replacement op), and the instructor managed to give us all a good class.
Have fun x