Firstly - you can only access languages that are already in your navigator. English is usually there as far as I know. New languages can be uploaded if required. i would ask a dealer or an experienced operator to do this.
From the begining, Press button M3 labelled MENU, this opens the MAIN MENU. Using M1 button select NAVIGATOR KONFIG and OK with M2. M1 down to CHANGE LANGUAGE - but you will probably see the German - SPRACHE WECHSELN. Press M2 to change (It should go straight to English) save with M3 which takes you back to the start.