Touchscreen acting up, registers touch randomly

Hi, My iphone 4 32gb , started acting up few weeks back, first suddenly it overheated in my pocket . Then i left it for few days switched off.

I updated the software to 6.1.3 and started using it, it worked fine for 15 days and now the touchscreen is playing up. It randomly registers touch, 70% of time touch location registered is wrong and sometimes registers touch even when i am simply holding the phone.

I dont have any service center near my place so need to repair myself.

Not sure what part might be playing up:

1. Battery

2. Digitizer

3. Logic Board

Looking forward for your advise.... Thanks.