The following sample reads a history record. You must get the unique key value for the history record to update.
//for this sample, it is assumed that the unique key of the target
History record to read is a String, "HIST_0011"
protected HistoryRepository historyRepository;
History readHistory = historyRepository.readHistory("HIST_0011",
getPropertiesToRead());
private List<String> getPropertiesToRead() {
List<String> properties = new List<String>();
properties.add("version");
properties.add("createdBy");
properties.add("createdOn");
properties.add("modifiedBy");
properties.add("modifiedOn");
properties.add("archivedOn");
properties.add("text");
properties.add("shortDescription");
properties.add("parentObject");
properties.add("categories");
return properties;
}