Nokia Lumia 520

Find "lock screen"

Slide your finger left on the display.
Press Settings.

Find "lock screen"

Press lock screen.

Select option

Select one of the following options:
Turn on use of phone lock code, go to 2a.
Turn off use of phone lock code, go to 2b.

2a - Turn on use of phone lock code

Press the indicator next to "Password" until the function is turned on.

2a - Turn on use of phone lock code

Press the field below "New password" and key in the required phone lock code.

2a - Turn on use of phone lock code

Press the field below "Confirm password" and key in the phone lock code.

2a - Turn on use of phone lock code

Press done to confirm.

2b - Turn off use of phone lock code

Press the indicator next to "Password" until the function is turned off.
Key in the phone lock code to confirm.

Return to the home screen

Press the Home key to return to the home screen.