An ESN Change is when you switch one phone to another.

For example, let's say you have a Huawei Ascend. You then purchase another device, let's say the LG Optimus C. You then want to switch from the Ascend to the Optimus. You request an "ESN Change" which will switch the phones in Cricket's system. This will mean the Huawei Ascend will stop working and your LG Optimus C will begin working. You just "swapped" the phones. Nothing else was done.

*By doing an ESN Change the ESN is changing in Cricket's system. Your phone's actual ESN (usually found under the battery) is NOT changing.*