You might not have to do anything, the nav will reboot after car beeing idle for 15 min or so.
To reset the nav and the rest of the car remove the ground from battery for a while 15 min or so
And it is highly recomended to update to latest OS, you will be amased how mutch better and faster it is

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X5 4,4i-06 Current
330Ci Cab-03 2007-2008
MB E55 AMG-03 2006-2007
Z3 2,8 Roadster-98 2006-2007
X3 2,0d-05 2005-2006
320d-99 1999-2005