Keep in mind that network attached storage usually has access control built in and is almost always managed using a web interface. Since it is a USB drive attached to your router, you might have to login to it to change your settings. You can find your router's IP address by doing this. Hold down your windows key on your keyboard (between ctrl and alt) and hitting "r". This will pull up a box that says "run". Type: CMD in that space and press enter. This will pull up a black command prompt. then type: ipconfig in that black box and hit enter. You will probably have to scroll back up and find it but what you are looking for is your default gateway. Lets say hypothetically that it is 192.168.1.1. You would open a web browser (like internet explorer) and type in something like this in the address bar and press enter:
http://192.168.1.1
Most routers have the default administrator username and password on the sticker on bottom. You would have to find your network attached storage settings.
Something else you might try, once you know your router IP, is opening another run box and typing in something like this:
\\192.168.1.1
Depending on the router and how it is configured, it may let you use windows explorer to browse through the data on that drive.
Hope this helps.