Steps
Go to Settings and click "Workspace Users"
Click on the User Name whose role you want to change
Click the Action dropdown next to their Role
Select a new role
change saves automatically
The member will immediately have their new access level
For board-specific roles, open the board and click "Share"
Change individual board roles using the same dropdown method
Notes
Owner has complete control over the workspace and all settings
Admin can manage users and permissions but cannot delete the workspace
Editor can create, edit, and organize boards
Viewer can only view boards in read-only mode