With many VTech phones, you simply press the down-arrow or - key while the phone is in standby mode.
Enter the model of your VTech phone into the search box at http://www.vtechphones.com/support/general/manuals to download a copy of the manual.
Since you neglected to specify the model of your VTech DECT 6.0 system, please enter the model number into the search box at http://www.vtechphones.com/support/general/manuals to download a copy of the manual.