how to set the folder's space size with C#,

public double SetNewPrefsForUser()
{
    try
    {
        byte inputChar;
        IsolatedStorageFile isoFile = IsolatedStorageFile.GetStore(IsolatedStorageScope.User |
            IsolatedStorageScope.Assembly |
            IsolatedStorageScope.Domain,
            typeof(System.Security.Policy.Url),
            typeof(System.Security.Policy.Url));

        // If this is not a new user, archive the old preferences and 
        // overwrite them using the new preferences.
        if (!this.myNewPrefs)
        {
            if (isoFile.GetDirectoryNames("Archive").Length == 0)
                isoFile.CreateDirectory("Archive");
            else
            {

                IsolatedStorageFileStream source =
                    new IsolatedStorageFileStream(this.userName, FileMode.OpenOrCreate,
                    isoFile);
                // This is the stream from which data will be read.
                Console.WriteLine("Is the source file readable? " + (source.CanRead ? "true" : "false"));
                Console.WriteLine("Creating new IsolatedStorageFileStream for Archive.");

                // Open or create a writable file.
                IsolatedStorageFileStream target =
                    new IsolatedStorageFileStream("Archive\\ " + this.userName,
                    FileMode.OpenOrCreate,
                    FileAccess.Write,
                    FileShare.Write,
                    isoFile);
                Console.WriteLine("Is the target file writable? " + (target.CanWrite ? "true" : "false"));
                // Stream the old file to a new file in the Archive directory.
                if (source.IsAsync && target.IsAsync)
                {
                    // IsolatedStorageFileStreams cannot be asynchronous.  However, you
                    // can use the asynchronous BeginRead and BeginWrite functions
                    // with some possible performance penalty.

                    Console.WriteLine("IsolatedStorageFileStreams cannot be asynchronous.");
                }

                else
                {
                    Console.WriteLine("Writing data to the new file.");
                    while (source.Position < source.Length)
                    {
                        inputChar = (byte)source.ReadByte();
                        target.WriteByte(inputChar);
                    }

                    // Determine the size of the IsolatedStorageFileStream
                    // by checking its Length property.
                    Console.WriteLine("Total Bytes Read: " + source.Length);

                }

                // After you have read and written to the streams, close them.
                target.Close();
                source.Close();
            }
        }

        // Open or create a writable file with a maximum size of 10K.
        IsolatedStorageFileStream isoStream =
            new IsolatedStorageFileStream(this.userName,
            FileMode.OpenOrCreate,
            FileAccess.Write,
            FileShare.Write,
            10240,
            isoFile);
        isoStream.Position = 0;  // Position to overwrite the old data.