When a release goes live, we publish release notes and other documents by running new builds on readthedocs. To actually change the release date that appears on the docs.edx.org page, you need to update an HTML file in edx-platform.
Step-by-step guide
(Original instructions follow these in case they're helpful as well. These steps created after a quick demo from btalbotR (Deactivated).)
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the edx/docs.edx.org repository. For more information, see Updating the docs front page (docs.edx.org).