This has probably been asked before so apologies if it has but as a newbie I would like to know if it is possible to update the maps on the rns510 using a usb stick or usb external hard drive?

No, its updated via DVD, unless you have a recent firmware in which case you can use a SD card.

Hi

I am using fw4120

its worth reading this thread

http://www.briskoda.net/forums/topic/325377-updating-columbus-maps-from-sd-card/?hl=%2Bcolumbus+%2Bsd+%2Bcard#entry3938296

it mentions a thread on GPSunderground , you'll need to locate that thread yourself as it has some links to dodgy software in it, but the guide is ok.

Thanks Mannyo