if you if you want to just to reimport, simple as Jim said
if you want to retain your existing library as is though I'd use the Rename/Move Copy tool, then choose the
Update database and point to new location (no rename) which is one of the choices in the drop downbox. That is if you have already moved all your files -- this is pretty simple if you kept the same (I hope) directory structure - make sure your serverPC sees the Nas and the filepaths first through windows of course. If you have not moved the files yet there is another similar option. If you have messed with the filepaths of the files, thats a bit trickier - but if its consistent you can use the Rename tool with a couple extra tweaks
Afterwards, you still will have to change your import options (autoimport).
There are other methods, but I like this one
Whatever, make sure you backup the library file before you do anything like this