An old thread, but I have just come across it after trying to work out how to do this myself, so for anyone still needing it, this is how you do it.

The MVE-M300P unit should have a USB coming from it to which a USB stick can be plugged in.
In the OP's case, its either missing or hidden I'd say.

I would remove the headunit and trace the cable from the back of it that goes to the M300P box. Then you will be able to see if the USB cable is there.
Once you have that sorted, you need to do the following:

1]Register on Naviextras (the site where you get the map updates from)
2]Download and install Toolbox
3]Turn on your sat nav, and plug in the USB stick
4]Choose collect info from unit and follow the instructions on screen.
5]Now start Toolbox on your PC and plugin the stick.
6]Toolbox will now connect to the site and tell you what updates are available.
On mine I had to install a firmware update first. This involved downloading it, unzipping onto the stick and then installing it in the car by turning on, plug in stick and choose install updates.
After it restarts, start again at step 3.
Close Toolbox and reopen it, then plug in the stick again.
Now mine said I had a map update to do, so am currently downloading that.
I imagine you then copy it to the stick, plug into the car and choose add updates

Hope that helps

Sounds like the other end of the USB cable isnt plugged into the sat nav box?
So Id check that first.
Just to clarify, was the memory stick freshly formatted and emtpy?

Just try to trace the cable back from the USB end, the other is just a micro USB connector that plugs into the sat nav unit.
The unit is meant to be mounted level, pointing forwards and in the centre of the car, so that should hopefully give you an idea of where it might be. Assuming it was installed correctly of course!
Mine sits on top of the transmission tunnel under the dash

I never said what car it was! I just found this thread when googling trying to sort mine out, and as I was already a member on here I thought Id reply to be helpful

You are correct in what you expect to have to do, which suggests something is wrong.
When you have it turned on, when you plug in a memory stick after a short wait it should bring up a menu.
The first thing to do is what I listed above in step 4 where you gather info from the unit.
This basically turns the memory stick into a proxy for the sat nav to be a go between from car to pc/laptop.
It should bring this menu up even with an empty stick plugged in, which is why I was wondering of the cable was plugged in at the other end.

Start from Copy Device Information from NVE-M300P to USB stick instructions here:
http://www.alpine.uk.com/support/firmware-map-upda... and you can see the screens you should be expecting to get when you plug the stick in