Read
this (<- click)Basically you bought yourself a wrong device.
Well, the Start 20 is not a bad device but it can only be updated via MyDrive, TomTom.
You might have a chance that your Start 20 is really a Start 20M, where the M stands for LifeTime Maps. That's a bit unlikely but not impossible because some people don't know what they've got or never get around getting what they are entitled to.
You also have a chance that your device has a right to a newer (not newest) map and that it will be offered to you.
If you need to buy a new map, you can wait for a time when TT offers 30 or 40% discount. Like they have done for about a month before last week.
In all cases you'll have to go to
[Please Register or Login to download file] , get the MyDrive software and register your device.