The problem is the Go300 only came with a 512gb SD card which was almost full when supplied all those years ago.
It's a pain if you haven't got a spare card laying around but as Simon says they are dirt cheap now.
Or you could go down the route that the £30 for the update will more than half pay for a new smaller slicker satnav which you will be able to install tomtom on and updates are easy found on the net free.
