ahoy @uppalasrila,

change is adding, replacing or removing something, it can be a new hardware or software.

Depending on the nature of that change it can be standard (pre-approved because it's happening frequently and is with low risks), emergency (reactive to some critical issue) or normal change.

for the normal and emergency changes there is a change advisory board to approve/reject such a change and it must be planned not to disrupt anything (after business hours, during weekend etc).

That's in a nutshell what change management does. Do you have any particular question about it?