How you change a Participant depends on whether it is your own organisation or another Participant in your ecosystem. You can edit your own organisation's details directly, while for other Participants you manage your relationship (link) to them rather than their core details, which they maintain themselves.

On the Participants List (Ecosystem Registries > Participants), your own organisation's row has an edit (pencil) action. Use it to update your organisation's details, then save your changes. The list reflects any visible changes.

For other Participants, you do not edit their core details (these are owned by that organisation). What you manage is your relationship with them: the relationship type and whether it is direct, using the Edit link action, or removing the link entirely.