updating maps on medion? :)

Hi there
I'm trying to update my maps on my medion (sorry, not sure which model, but it's definately not got an in built gps, it uses the wired receiver that you stick on the dashboard). The maps on there are "England and Ireland" and the maps i want to stick on there are "British Isles". The map i have is just one file, (.map) and the maps on the mmc card (and the medion software bundled with the pack) are .sfs files, along with some other smaller files and other directories too (like db, and kwl). Is there anything i can do to put this new software on? Or is there any alternative gps software i can use? Thanks in advance
-Mark