Yes! In fact that's the safest way... also you probable won't have enough free space without removing it first! If the new map is much larger than the old one you can gain space by removing all the other languages you don't need (there's something like 20+) also there will be just as many 'keyboards' for all these countries.
With your satnav plugged in via the USB lead it should open up in explorer so you can have a look inside, the maps are in the garmin folder, the other method is if you're unsure to get a 1 -2gb SD card, make a new folder called 'Garmin' then put the map in this folder.
Once you've switched the satnav on with the card already installed go to map, then info, and have a look and add a tick to this new map. Then when you switch the sat nav on it will always default to the latest map.
Once you're happy that the new map works, then it can be renamed and you can swap it with the internal map, but as you say DON'T delete the old map, drag it into a new/spare folder on your computer.
