You might need to select the button and drag it to the left. If you want to see how the rollover effect works, in the Layers panel, click the eye icon next to the Web Layers layer to make the slices invisible. Select the Preview tab in the image dialog. Adding the Swapped Image From the Layers panel, select the Frame tab. Frames are like Layers but slightly different.
Frames can contain hidden images, such as swap images.
We'll create some text, add a Slice rectangle to contain it, and place it in its own Frame. If you select frame 1 and then frame 2 you will notice the button switches from A to B. Select Frame 2 by clicking the Frame 2 title area. Select the Layers tab, press the small triangle-shaped arrow and from the flyout menu select New Layer. Make sure the Share Across Layers box is not checked. Select the Text Tool and click in the page next to the A button to open the Text dialog.