To Delete a Function Key Definition

Select Function Keys from File > Settings > User .
The Function Keys dialog opens. The title bar identifies the open function key menu.
Do one of the following:

Select a function key from the list box.

or
In the Function Keys group box, turn on the Ctrl, Alt, and/or Shift check boxes and select the desired function key from the Function Key Drop-Down List.

or
Using the keyboard, press the desired function key and the <Ctrl>, <Alt>, and/or <Shift> keys.
Press the <Delete> key.
Click Save to save the changes and close the dialog.