if you are asked to save this measurement. Uncheck the curve you
want to erase from the legend list by clicking at it. In the example below
Meas. 9 is unchecked.If you have performed a measurement that you are not
satisfied with, you can click if you are asked to save this measurement. Uncheck the curve you
want to erase from the legend list by clicking at it. In the example below
Meas. 9 is unchecked.
To erase the curve from the plot, go to Plot->Erase
Curves..... Now make sure 
is selected as shown below.
Click 
in
the dialog to erase the curve.