When you add new images to GIF they appear at the end of the List of images. You can move them to any place of the list.
To move wanted image up (down) in the list select menu item Image / Move Up (Image / Move Down) or click the toolbar button () of Standard Toolbar.
Note: you can also change position of an image in the list by dragging the list item to new place, using mouse with pressed left button.
To remove wanted image from the list select menu item Image / Delete or click the toolbar button of Standard Toolbar.
Note: you can delete image group selected by checkboxes in the List of images.