The BOSSA program is found on your Windows Start menu. You should see a main window that looks like this:
Click on the the Auto-Scan button in the Serial Port group box to find your DRO-550. If no DRO-550 is found, then you should open your Windows Device Manager and look at the entries under the Ports (COM & LPT) list. You should see an entry for "BOSSA Program Port" (or possibly "GPS Camera Detect" for Windows 7). If not, check your DRO-550 board and try plugging it in again after rebooting your PC.