This should give you an idea on how to perform some of the steps. SSL certificates are crucial as well as you won't be able to install against an existing database without them.
VMware KB: Backing up and restoring vCenter Server 4.x and 5.0
With 5.1 you will also need to backup SSO and the Inventory Service. License keys are actually stored in the ADAM database.
VMware KB: Manually backing up and restoring the vCenter Server 4.x and 5.x ADAM instance data
VMware KB: Backing up and restoring the vCenter Single Sign-On (SSO) configuration