Power off your Samsung Galaxy SL (GT- I9003) to start in recovery mode.
Once you have power off the phone, press and Hold Volume UP and Home button. Make sure you have hold volume up, don't press in the middle of the volume buttons.
Now keep pressing these two buttons(VOL UP + HOME) and press power button for 2-3 seconds. Release only power button, but keep pressing Volume Up + Home Button, until you see the screen shown below.Once you see recovery screen release the Home button else your phone will restart as first selected option will be restart and pressing home will make that happen.
In the recovery mode, volume up & down act as a up scroll and down scroll buttons, by pressing Home button you will be able to click the selected option.