Only managers can change the roles of other members in a Groove workspace. Additionally, roles can only be promoted.
You can point at any name in the Members list to see that member's role in a status window:
To change a member's role:
In the workspace, right-click the member and then click Roles...
In the Change Role dialog box, click the new role for this member, and then click OK.
If you want to change the roles of several workspace members at once, open Workspace Properties in the Backstage view, and then click Roles. Click Change Role... to open the Change Role dialog box. Change roles for members, as needed, clicking Apply after each role change.