How to convert the spot levels to contour lines level?

If your using LDD I believe you have to recreate the points at new elevation. In my company we use Civil 3D and we can raise/lower them quite easily. Select points right click your mouse Select datum and type in the elevation you would like to raise/lower them by.  You can try that in LDD I am not sure what version of CAD your running, but that should take care of what your wanting to do.  I hope that helps.