The user management can be found at any level by clicking the settings cog and selecting "users" from the dropdown list.
The users screen will show all platform users associated with that organization.
New users can be created, existing users deleted, passwords reset to their email address or their details edited.
When creating a new user or editing an existing user, the organizations they are associated with can be selected.
When editing a user, a default organization can be selected (usually an owner organization).
Users Overview Page
Create New User Page
Edit User Page