You can't delete the default MC library, which is the library stored locally on your laptop at a location something like "C:\Users\[UserID]\AppData\Roaming\J River\Media Center 23\Library". The new library you created will be stored somewhere else. You can see where it is by clicking on the library name under "Playing Now > Playing from [PC Name] Local Library > [Name you gave your new Library]", top left corner of MC in Standard View.
But as you are a light user, if you aren't fussed about the old library just staying there, since it isn't very big, then just go to;
Tools > Options > Startup > Library, and untick "Always load default library". Then you just need to open your new library once, if it isn't already open, and from then on MC will open the last library that was open, which is your new library. There are other things you could do, but that is easiest.
Also as a light user, I assume you haven't customised anything in MC, so you didn't lose anything by reimporting the files. If you did lose some functionality you wanted to keep, like customised views, then speak up and I will help you fix you old library that still holds that functionality.
What I would need to know is;
Was the old drive that was connected to your router accessed via a drive letter? If so, what was it?
Which drive did you put the media files on to on your laptop? The C: drive?
Did you just copy the whole directory structure from the old drive to the laptop drive, or make some changes to the structure?