Download WinRar by clicking
Here and use that to extract all the files in the CAB download you have stored directly to the drive letter associated with your TomTom device, Please note the screen shots below were from a different Navcore instal to a different device but you should be able to follow the process:
As always backup the unit
BEFORE trying any update/ roll back just in case it goes wrong.
Double click the CAB file upon which one you downloaded and winrar will fire up, use the mouse to select all files and folders then click "Extract To"
Locate the drive letter associated with your TomTom and click it, make sure the Overwrite mode is selected to "Ask before overwrite", then press "OK"
When the dialogue box pops up saying "Confirm File Replace" click the "Yes To All" button.
Sit back and watch the progress bar, with a good USB2 connection a Navcore installation will take around 2 minutes.
When its finished the update use the "Safely Remove Hardware" icon from the Task Tray and remove the lead from the device.
Let the device boot up and tap the sat strength meter (lower left) followed by the version box, the resultant screen will confirm the version installed is as expected - Mike
PS Pictures paint a thousand words, thats why it took me a full 7 minutes longer to answer!!!
Strange how both answers say more or less the same thing - someone might get the idea we both went to the same school of "How to fix a TomTom"