Delete blank node from ontology through SPARQL UPDATE

I am storing some data in my ontology model made in protege with help of a SPARQL UPDATE 'insert' operation. Below is the update query.

PREFIX test: <http://www.semanticweb.org/muhammad/ontologies/2017/2/untitled-ontology-14#>
insert {
  [] test:Kpi_Variable ?s ;
     test:hasValue_ROB4 ?p ;
     test:hasTime ?now .
}
where {

    values (?s ?p) {
        (test:Actual_Production_Time 33)
    }
    bind (now() as ?now)
}

It stores in the rdf graph in the following way:

[ test:Kpi_Variable   test:Actual_Production_Time ;
  test:hasTime        "2017-06-02T14:40:33.187+03:00"^^xsd:dateTime ;
  test:hasValue_ROB4  33
] .

Now I want to delete this blank node with the 'delete' operation. I have tried many ways but that didn't work. Any Suggestions?