It is very easy to update the software. check what version you have now - in the 'Set' menu on top right hand side of screen it shows the SW version.
The first digit shows what generation nav you have.
eg: 3-1/63 = Mk3, version 6.3

the current versions are:
3-1/63
4-1/91

Otherwise, ifyou wish to change the small-screen to the wide-screen then you need to buy a new one on ebay