How you leave an Organization depends on what permissions you have been granted. If you have been granted Organization Manager or Organization Admin Manager permissions, you can remove yourself through the Member Management interface. Otherwise, you will have to request your removal.
For a reference on Organization Roles, see this article.
This article will show you both ways to leave an Organization.
As an Organization Manager or Organization Admin Manager
First, navigate to your Organization's page by hovering over Manage in the Top Navigation Menu and selecting Manage Organizations. This will take you to the Organization Management page.
Search and filter for your organization, and then select the Manage Members button under its listing. This will take you to the Member Management interface.
For a more detailed run-down on finding your Organization, see this article.
On this page, you will find a full list of members and managers in your Organization. Search for yourself, and click the Red Trashcan Icon next to your name.
This will remove you from the Organization.
As Any Other Role
First, click the Grid icon in the Top Navigation Menu. In the grid menu, select Organizations. This will take you to the Organization listing page.
Search and filter for the Organization you want, and then click on its title. This will take you to the Organization's profile page.
For a more detailed view on finding your Organization, see this article.
Under the People section of the page, you will find a list of key members of the Organization. From here, you can look up one of those members in the Inbox interface, and manually make your request there.
For more information on sending messages, see this article.
If you are unable to locate a suitable contact within the Organization, get in touch with us through the Intercom messages. We'll be happy to help.