This helper will do the trick:

    public static class FileHelper
    {
        public static void MoveWithOverwrite(string sourceFileName, string targetFileName)
        {
            if (File.Exists(targetFileName))
            {
                if ((File.GetAttributes(targetFileName) & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
                    File.SetAttributes(targetFileName, FileAttributes.Normal);
                File.Delete(targetFileName);
            }
            File.Move(sourceFileName, targetFileName);
        }
    }