How to change touchscreen

kiran, you can download the complete service manual for the k850i from here. It will tell you all you ever needed to know about your phone. Also, if it is your touch screen that is not working, but otherwise everything else seems to be okay, delete some (or all ) of your messages, txt, and pics. Apparently the SE k8501 requires a lot of memory to function. It may hang up if it encounters RAM trouble. Also check the flex cable to make sure it is okay. Anyhow the manual will let you test your phone completely for further trouble shooting.Good Luck.