Add a member
Go to account.conduktor.io, and sign in to your subscription.
Ensure you have either an "Owner" or "Team Member" role. Please see here for an explanation of these roles.
Once signed into your subscription you should see a screen similar to the below screenshot.
You can click on the "Add a member" button, as shown in the screenshot below.
You will then have to provide the "Name" and "Email" of the new member, and they will be added.
Revoke a member
To revoke a member, ensure you are signed into your subscription and have either an "Owner" or "Team Manager" role.
Then, on the subscription page itself (shown above), click on "Revoke" which will be to the extreme right of the user in question.
You will then revoke this user and see them in the "Removed Members" section at the bottom of the page, in case you ever need to re-add them.