Rename the Navigon.ipa to be a zip. Unzip. Show package contents for the Navigon bundle, delete the maps you don't want. Zip back up (make sure the folder structure is the same) and rename to .ipa. Then remove and reinstall the application.

You may need to remove the original out of iTunes then double click the new one to get your modified version installed.

KEEP A BACKUP.

gilesjuk,
ok thanks for the qucik reply I'll try it when I've got a little time to spare. Up to now I've always downloaded the Navigon straight onto the iPhone i.e. not onto iTunes first.

Regards

jawdrops