garmin nuvi 54LM?

I tried to download a map update on my sat nav but nothing happened when I clicked the 'download now' button waited 15mins, nothing told me it was downloading/ed. Trying again a message tells me its downloaded find it on your computer and complete download. Where to look for the map?
I am a novice on computers help!!!!
Windows 7 ultimate.
Thanks

bob
June 2013