public class ContactDeletesa implements database.Batchable<sobject>{
public database.QueryLocator start(database.BatchableContext BC){

    String Query='select id,lastmodifieddate from contact where level__C='First' ';
       return database.getQueryLocator(Query);
}
public void execute(database.BatchableContext BC,List<contact>scope){
    List<contact>conList=new list<contact>();
    for(contact co:scope){
            co.level__C='1';
           conList.add(co);
    }
    database.update(conlist,false);
}
public void finish(database.BatchableContext BC){

}