Workspace Administrators and Owners are able to change the roles of Users within their workspace. To do this, click on Manage Members, find the member you wish to make a change to, and click the triple-dot menu.
The different roles for a workspace are described in the Workspaces Overview.
Members can be upgraded to Admin:
Members can be upgraded to Owner:
Members can be upgraded to Primary Owner. Transferring to Primary Owner is a one-way street and cannot be reversed, so the current Primary Owner must acknowledge this before proceeding.