Remove unused FtpUploadHelper overloads and incporporate localFilePath validation test in "main" FtpUploadHelper overload.
Convert FtpDownloadHelper(Uri, string, string, string, FtpType) to use System.Net.FtpClient and delete obsolete FtpDownloadHelper(IFtpWebOperation, string, string, string, FtpType) overload.
Convert GetFtpDownloadLength(Uri, string, string, FtpType) to use System.Net.FtpClient and remove obsolete GetFtpDownloadLength(IFtpWebOperation, string, string, FtpType) overload.
Convert FtpCheckConnection(string, int, string, string, string, FtpType) to use System.Net.FtpClient and remove obsolete FtpCheckConnection(IFtpWebOperation, string, string, FtpType) overload.