def rename_header(df):
    """Rename as follows
       Chr -> chr
       Pos -> pos
       Chr_Allele -> ref
       Alternative_Allele -> alt

    Args:
        df (pandas.DataFrame)
    Returns:
        df (pandas.DataFrame)
    """
    df.drop("Type", axis=1, inplace=True)
    df = df.rename(
        columns={
            "Chr": "chr",
            "Pos": "pos",
            "Chr_Allele": "ref",
            "Alternative_Allele": "alt",
        }
    )

    return df