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.