I have forgot how to modifying line properties using surveyors units on an exciting line in corelcad. I see the angle I want to change in the properties box but will not let me change it. Please can any one help.

I have forgot how to modifying line properties using surveyors units on an exciting line in corelcad.
I see the angle I want to change in the properties box but will not let me change it.
Please can any one help.