JB version - how to tell

Hey everybody,

A couple questions:

1) I have installed JB on my kindle quite some time ago; is there a way to tell - by inspecting local directory, looking on KUAL or anything else, which version of the JB I installed?

2) In case it is not the most recent, is it possible to "update" JB by simply installing the most recent one (fw version 5.4.5.1) on an already jailbroken device?

Thanks