You can manage the members from the organization's people settings. To get to this section, click on the organization name from the lower left side of your dashboard page, then select “People tab”. See the screenshots below for reference.
On the “People tab” page, you will have the option to send an invite, change roles, or remove users. Please see the screenshots below for reference.
Invite/Add new user
Click on the "Invite New User" button to send the invite to the email address of the new member you want to add on the organization.
Change role/ownership
Click on the “dropdown list” next to the member's name to see the option to change roles. Please note that changing the ownership can only be done by the current owner of the organization.
Remove a user
Click on the "three dots icon" next to the user status then select "Remove user".