A few pointers to get in the right direction, link to FAQ page is at the end of this post:
1/ Make a full backup of the device using Windows Explorer - NOT TOMTOM HOME as it isn't reliable enough see FAQ
#1 2/ Connect the device to the Home software and register the unit with a different e-mail address to that used with your other device DO NOT re-use the old e-mail address and don't consider transfering it as it will probably screw up your Live services account (its not worth the risk) - If you don't have a second e-mail address simply make something up in the e-mail address format and the server will accept it.
3/ Use Home to update the application to the latest available.
4/ Use Home to update the map to the latest version for free by going to Tools/ Use Latest Map Gaurantee (Make sure your computer is using a wired connection to the internet don't use WiFi as its known to cause issues) - I would wait until the end of the month to use the Latest Map Gaurantee as you have 28 days in which to use it and a new map should be released by/ before the end of the month.
5/ For the POI files in your old map folder simply copy the .ov2 and .bmp files from the United_Kingdom map folder on your old unit to the Western_Europe map folder on the new device.
6/ Convert your Favourites to an ov2 Custom POI category as copying the file from a 300 to a 750 won't work and will cause issues, see FAQ
#15
The FAQ page is on a different web site (Sorry Martin but I think the easy way is a link to the info the chap wants rather than a huge post on here) can be found by clicking
Here - Mike