private void SaveTempFile(HttpPostedFileBase file)
{
    //get the uploaded file name
    string fileName = file.FileName;

    //get temp directory path
    string tempPath = Path.GetTempPath();

    //init the file path
    string filePath = tempPath + fileName;

    //if the path is exists,delete old file
    if (System.IO.File.Exists(filePath))
    {
        System.IO.File.Delete(filePath);
    }

    //and then save new file
    file.SaveAs(filePath);
}

private async Task SaveTempFile(string fileName, long contentLenght, Stream inputStream)
{
    try
    {
        //firstly, we need check the container if exists or not. And if not, we need to create one.
        await container.CreateIfNotExistsAsync();

        //init a blobReference
        CloudBlockBlob tempFileBlob = container.GetBlockBlobReference(fileName);

        //if the blobReference is exists, delete the old blob
        tempFileBlob.DeleteIfExists();

        //check the count of blob if over limit or not, if yes, clear them.
        await CleanStorageIfReachLimit(contentLenght);

        //and upload the new file in this
        tempFileBlob.UploadFromStream(inputStream);
    }
    catch (Exception ex)
    {
        if (ex.InnerException != null)
        {
            throw ex.InnerException;
        }
        else
        {
            throw ex;
        }
    }
}

//check the count of blob if over limit or not, if yes, clear them. 
private async Task CleanStorageIfReachLimit(long newFileLength)
{
    List<CloudBlob> blobs = container.ListBlobs()
        .OfType<CloudBlob>()
        .OrderBy(m => m.Properties.LastModified)
        .ToList();

    //get total size of all blobs.
    long totalSize = blobs.Sum(m => m.Properties.Length);

    //calculate out the real limit size of before upload
    long realLimetSize = TotalLimitSizeOfTempFiles - newFileLength;

    //delete all,when the free size is enough, break this loop,and stop delete blob anymore
    foreach (CloudBlob item in blobs)
    {
        if (totalSize <= realLimetSize)
        {
            break;
        }

        await item.DeleteIfExistsAsync();
        totalSize -= item.Properties.Length;
    }
}