Which estimates are used for release planning?

Release planning uses the rough estimates on backlog items, in the "Rough estimate" field of each backlog item. This way, you can add rough estimates on backlog items early on, during your release planning and high-level backlog management. Then, when a backlog item is ready to go into a specific sprint, or a Kanban board, you can do the detailed and more accurate estimation needed for that, and enter detailed estimates in the "Estimate" field of the backlog item or its tasks.

Rough estimates are completely separate from detailed estimates, and you can adjust the rough estimates independently of the detailed estimates.