Make a full backup of the device to your PC by copying all the files and folders from the unit using Windows Explorer.
Download and install the latest version of TomTom Home software to your PC, try
Here
Update the application on the device using Home, this will probably have to be performed twice, the first part updates the device to 8,300 and the second time you run the update it will take the device to 8,302 which is currently the latest available. To check the software and map versions on the device tap the sat strength meter (lower right corner) then the version box, the resultant page offers lots of information about the device.
With the device running the latest software connect it to Home and this time press Tools/ Use Latest Map Guarantee which should download and install the current latest map for free, the new map is v825.
With the device fully upto date you need to make another backup of the device to your computer, again usew Windows Explorer for this.
All the above is done for free, once you have the latest map consider joining the map update scheme which is a cheper way to get the next four map updates - Mike