The release management pack is basically a set of design transfer iles which create a standard Release process and associated objects. From memory it is no longer a chargeable option and comes in the out of the box database. If yours is an older system where it hasn't been imported in, you may need some consulting help to get it to go. Release is different to Change; different workflow and so on, but you could product a perfectly good release process within the change domain. The route you follow depends on your needs and how close the LDSD Release process is to what you want. Time for a chat to your account manager I think.
You can view the Release process design on page 56 of the guide below. This guide shows the 7.5 version of the process: