Opera gives you the opportunity to select the icons that appears on its toolbar. All you have to do is right-click the Main bar and select the 'Customize Toolbars' option from the pop-up menu. In the resulting dialog box, you can review the large and small icons, and drag the icon you want to use onto the toolbar.
To remove icons form the toolbar, right-click on the icon you no longer want and select the 'Remove From Toolbar' option from the pop-up menu. The icon should disappear immediately.