The reason why I want to change the screen is because it full of dusts. After I replaced it, it was really nice. But after couple month, dusts came back again, so I just switched to 4s.
Well, actually, it was much easier than I thought.
The only problem about this is that the hard drive temperature sensor cable. Even I bought the same brand HD, it still doesn't work. So I have to install fan control to control the fan speed.
But other than that, it works very smooth. The speed is great.
Thanks, ifixit. The home tech toolkit is great and really helpful.