I made a reverse radial gradient to look like "sunlight" and I would like to move it to the top of my image to appear like the light is coming from above, but it won't allow me to move the radial gradient anywhere. I have CS6. Help please :)

I made a reverse radial gradient to look like "sunlight" and I would like to move it to the top of my image to appear like the light is coming from above, but it won't allow me to move the radial gradient anywhere.  I have CS6.  Help please