var templateLibraryDocumentOutputPostAction = portalContext.TemplateLibraryDocumentOutputPostActions.Where(tldopa => tldopa.TemplateLibraryDocumentOutputPostActionId == Guid.Parse("00000000-0000-0000-0000-000000000000")).FirstOrDefault();	

templateLibraryDocumentOutputPostAction.Name = "New Name";
templateLibraryDocumentOutputPostAction.ValueToChange = value;

portalContext.UpdateObject(templateLibraryDocumentOutputPostAction);
portalContext.SaveChanges();

var url = "http://portal.xpertdoc.com/odata4/v6/TemplateLibraryDocumentOutputPostActions(00000000-0000-0000-0000-000000000000)";	
	
var values = new Dictionary<string, string>
{		
				{ "ValueToChange", "Value"},  
				{ "Name", "New Name"}	
};
var value = await Update(url, values);