To start off, you need to launch YaST. You can use the menu, or you can type in the following into an Alt+F2 prompt:
Click Software, and then Installation Source.
You should see a list of the software sources, with the cd/dvd line at the top.
To enable or disable one of the sources, just click the Source Settings drop-down button, and then click Enable or Disable.
You should disable the cdrom line, and enable the other two.