If you have loaded the UTM layout by mistake, it is easy to change it back to the standard layout. (or if you have the standard layout, and want to load the UTM layout, the process is the same).
The screens shown here are from an HN7 Navigator, but the process is the same for the other models.
Tap the Settings button on the right hand toolbar.
Tap the Load Layout button on the Settings screen.
Wait for a short period (5-10 seconds) for the layout to load.
After loading the standard layout file, OziExplorer will not display the UTM grid reference in the top-right corner of the map panel.