For starters (as Delta_G stated), you need to clear the lcd screen before writing any new numbers to the screen. This is because if you write number 11 and then write 2 without clearing the screen first, you might see 21 or 12 instead of just 2.
Also, you might want to git rid of the delay() calls. Rarely is delay() needed. See the tutorial "Blink Without Delay" if you need to do anything in terms of timing.