Begin by selecting the cabinet that you want to change the top panel for.

Look for the menu labeled "Cabinet" on the right of the design panel. It would be arranged in a vertical order as Cabinet>Partition>Shutter System>Shutter> Panel etc. Click on it to access the settings related to cabinet.

Within the "Cabinet" menu, you will find the "Carcass" option. This option will be available in "Construction" section.

Click on the drop down menu to access the various options available in which go to the "Railing Options". In "Type" select full and the top panel of the cabinet will change to full panel.