Difference between change mgmt & release management

Let's start with "Release Management" is the process of managing Product Releases, Process Releases, or Services Releases, from inception through to deployment and maintenance, post deployment. This includes the build, deployment, installation, instantiation, execution, teardown, and rollback of releases in each and every environment (e.g. Development, Systems Integration Testing, User Acceptance Testing, Production, etc.) (NOTE: Most companies usually only relate Releases to Products and not to Processes and Services, however, more and more teams are starting to realize that they need to manage Process and Service improvements, incrementally, through versioned iterations, like they do Products.)

"Change Management" is the process of managing individual or groups of "Changes" from inception, through to deployment and maintenance, post deployment. Again, this includes the build, deployment, installation, instantiation, execution, teardown, and rollback of changes in each and every environment (e.g. Development, Systems Integration Testing, User Acceptance Testing, Production, etc.)

"Change Management" is usually a subset of Release Management. Most mature organizations will increment the Release version if there is at least one new Change that is required, after a Release has been frozen.