Depending on its age, it will or will not have been accompanied by a software disc which will allow you to access the company website via your PC, plug in your satnav, and download updates.
From the sound of your enquiry, it appears your device may be too old for the facility, in which case you will need to replace it.
The TomTom is excellent - with upgrade software included. Buy from Halfords, they'll demo and install it for you for free.