Can I change form black to white

Yes. Older iPhone 4 can have proximity sensor problem. This can be a major hassle with the new white screen. Also if you are a purist, the white iPhone has a white charging dock port and white headphone jack port. This is a fun conversion if you know what you are doing. But since you are asking this question to begin with, the first time replacing an iPhone 4 screen is difficult. There are risks that can permanently damage the iPhone. If the screen is cracked or needs replacement, I say go for it. If the iPhone is working perfectly now, there are definite risks.