Navigate to Settings > Staff Management. If you do not see this section your user may not have the correct permissions to manage staff. Once in this settings area find the role you wish to edit and select Actions > Edit from the list.
Here you will see two fields.
Role is the name of the role, such as "guide", "bartender", "dive master", "captain", etc.
Short Description is an optional field to describe what this role does.
Select Save Changes after you are finished editing the role.