Here are the steps:
1) Download the encoder build that includes the migration feature to copy a shared release into v8. You can download that build here.
2) Under Release Pending or History list, search for the release that you want to migrate.
3) Right click on the release and select share release.
4) Set up and complete release sharing in v4
5) Select Migrate to V8
6) A copy of the 'root' release and asset a long with all equivalent metadata is made in V8
7) A v8 release sharing schedule is made in v8 making a best-effort to duplicate the release sharing done in v4
8) When the process is complete a notification email will be sent to the encoder user who migrated the release.