Hi Tony
This is very easy
There is a slide off section at the opposite end to the antennas. In the first 20 or so Rosettas to be shipped the sticker was wrapped around the whole case. After the first 20, and all new ones that are delivered we cut the sticker along the two interfaces so that this end section is easier to take off.
Yours sounds like one of the first units. So look at the Rosetta and take a sharp hobby knife and cut along the top and end joints through the sticker. Be carful.
When this is done you will be able to slide off the end section and gain access to the USB slots.
Regards
Keith