If you'd like to assign/change the roles within your Curatr you should:
Click on 'Users' in the top menu bar. A list of all your users will appear.
Search for the user whose role you wish to modify. Once you have located them click either the eye (User Information) or pencil (Edit User) icon (it doesn't matter which you click as they will both allow you to undertake the next steps)
Click on the 'Roles' tab.
You will now be taken to a screen containing information/options relating to that specific user. On this screen you can now see a row of tick-boxes that relate to the various roles. You can now tick / untick the boxes/roles as you wish.