Iphone 4S screen replace is not easy. There are so many tiny parts which all are important and all them individual functionality.
Step by Step guide for iphone 4S disassembly:
1. Power off the phone
2. Remove sim tray and sim card
3. Remove 2 screws from bottom of the phone.
4. Slide off the back cover
5.Remove 2 screws from Battery connector
6. Take off battery from the phone
7. Remove the screws from the charge port Ribbon
8. Disconnect the charge port Ribbon and full it aside
9. Remove 4 screws from camera button area
10. Remove the metal cover and remove screw under the metal cover
11. Disconnect all the connector
12. Disconnect antenna Ribbon from bottom of the phone
13. Remove 2 screws : one is top and another one is bottom
14. Now remove screws which are holding the motherboard
15. Take off the vibrator
16. Remove 2 screws from the speaker
17. take off the speaker
18. There are 4 screws : one in each corner of the phone
19. Remove 6 screws : 3 each side of the screen frame
20. Now remove the screen
