1. Choose correct flash file(s).
2. If you have PIT file chosen, then you must check "Repartition" option.
3. If you have one file firmware, then you must check "Use one package file" option.
4. Check flashing options if needed (Repartition, EFS clear, Boot update).
5. Power on phone in download mode (turn off phone, press vol.down + home + power).
6. Connect phone to PC with USB cable, install drivers if needed.
7. Press "Flash" button.