You can change the icons around to your desire whenever you like. You can change the order, move icons from one screen to another, and change which and how many icons are in the lower section (not more than four).
You may have noticed that you have more than one screen for icons. You can move from one to another by pressing your finger to the screen and swiping across to the left or right to spin through the screens. There are small white dots along the bottom that shows you which screen of icons your on. The lower row stays the same as you move from screen to screen.