Archive.DeleteEntry

public Archive DeleteEntry(ArchiveEntry entry)

using (var archive = new Archive("archive.zip"))
{
    while (archive.Entries.Count > 1)
        archive.DeleteEntry(archive.Entries[0]);
    archive.Save("last_entry.zip");
}

public Archive DeleteEntry(int entryIndex)

using (var archive = new TarArchive("two_files.zip"))
{
    archive.DeleteEntry(0);
    archive.Save("single_file.zip");
}