We recommend reading 'Rules that govern permissions and roles' before reading this article.
Roles can be assigned at two levels, workspace and project. However the workspace role can only be assigned at the workspace level.
At a workspace level
To change an existing workspace member's roles, simply navigate to 'Members', at the workspace level. In this menu, select the desired user you wish to manage. The side bar that displays on the right allows you to either change this users workspace role or add them a project with a specified role. To do either of these tasks, select the desired role/project and select update workspace role/add project role.
To change a users existing project role, you must first remove them from the project by selecting the cross icon next to the project name and re-adding them with the desired role. If some of these functionalities are disabled, this may be due to insufficient rights to perform these actions by the currently signed in user.
At a project level
To change an existing project member's role, simply navigate to 'Members' at a project level. Then, in this menu select the desired user you wish to manage. The sidebar that appears allows you to manage that users project role and environment access. To manage environment access simply toggle access on or off using the switches located below the project role. Note that a project role is applied to all environments within that project, however user permissions vary depending on if the environment is a critical or non-critical environment. To learn more about permissions see here.