Refresh/update of library content?

Refresh/update of library content?
I would like to be able to change folder names etc, on my drive where I keep my music files, and then be able to update my music library in songbird. When I try to do so, the songs are still displayed but they can't be played - most likely since the pathway to the file has changed.

I.E. I have several folders in my "Music" folder on drive J:\.
Let's say that I want to change the folder name "J:\Music\crap\" to "J:\Music\sorted crap\".
All the songs in the folder "J:\Music\crap\" have already been added to the Songbird library by the function "File >> Import Media". After changing the folder name to "sorted crap", I want to refresh my library in Songbird. How can I do that? How can I get it to work?

How can I have songbird keeping track of changes in my Music-folders?
I experience the same problem as in iTunes - it is impossible to get rid of songs that no longer are valid due to changes in folder structure. Even worse, I can't even add the new path since Songbird seem to ignore duplicates (the files under the new pathway are added later and therefore they are ignored!?).

Someone help me out please!

Br
Anders