There is no simple way of doing this. I recommend using the Excel Import to remove resources. Please refer below on how to set up the Excel file. What you need to do is get the list of work items and the ID and just remove the user in question from the "Resources" field. If there are multiple resources, you will just keep the names of the resources on the sheet.
Managers on the other hand, is a little more tricky because you cannot remove a manager without replacing the manager if there is only one manager on the work item. This would require customization as a custom action would be best for this one. I recommend using the customization forum for this.
Column A Column B