Once we have deployed a stack and the resources are running, there is a possibility that we will need to change those resources. Whether it is through optimization or through the normal application life cycle, the need for changing a stack is almost a given for any deployment. Change sets help us with delivering updates and changes to the stack that we have deployed in our AWS account. 

With change sets, we create changes that we would like to perform on the environment we deployed. Once the changes have been created, we can run a comparison against our existing stack and get a detailed report of how these changes will impact the stack. There are three types of changes in any CloudFormation deployment:

• Non-disruptive updates: These operations don't have impact on running resources, for example, changing CloudWatch alarms within a template.
• Disruptive updates: These operations disrupt running resources for a certain period of time, for example, changing the instance type will require a reboot.
• Replacement updates: These operations terminate an existing resource and deploy a new resource with a new ID, for example, changing an RDS engine from MySQL to Aurora.

With change sets, we get a detailed description that can give us a deeper understanding of which kind of update is taking place and hence we can determine the broader impact of the change set's execution on our application. Once we are happy with these changes, we can execute the change set and the CloudFormation service will deploy the changes.