If you are looking to do it yourself, this snippet will retrieve all instances in chunks and deletes them bit by bit, so the script doesn't timeout or run out of memory.
Deleting history should be as simple as replacing "domHelper.DomInstances" with "domHelper.DomInstanceHistory".

var domHelper = new DomHelper(engine.SendSLNetMessages, "mymodule");

PagingHelper<DomInstance> pagingHelper = domHelper.DomInstances.PreparePaging(new TRUEFilterElement<DomInstance>());

while (pagingHelper.MoveToNextPage())
{
    List<DomInstance> dataTypes = pagingHelper.GetCurrentPage();
    foreach (DomInstance dataType in dataTypes)
    {
       try
       {
          domHelper.DomInstances.Delete(dataType);
       }
       catch (CrudFailedException e)
       {
          engine.GenerateInformation(e.ToString());
       }
    }

    engine.KeepAlive();
}