This tool takes in the input of your current plan ( postpaid or prepaid ) along with the kind of usage you have ( see snapshot below ) suggests you plans available with other mobile operators. For example I am using Vodafone Prepaid plan and this tool suggested me similar plan in Kolkata which I can opt in.
The main idea of Change My Network is to ease you with change of mobile operator once the Mobile Number Portability (MNP) is introduced in India which was supposed to come this April. It might take 7 days for change of operator and includes a minimal charge of 19 Rs. However this seems to be coming after October but we will have to wait for final confirmations from the TRAI.