The script is based on answer from https://social.technet.microsoft.com/Forums/en-US/fb1c9421-be23-4521-83d7-967396052021/azure-blob-change-tier-to-archive-via-powershell?forum=windowsazuredata
The $blob.ICloudBlob.SetStandardBlobTier() operation uses Methods of scalar objects and collections to retrieve properties and execute methods for each item in the $blob collection.
$StorageAccount = ""
$StorageKey = ""
$Container = ""
$ctx = New-AzureStorageContext -StorageAccountName $StorageAccount -StorageAccountKey $StorageKey
# Get all the blobs in container
$blob = Get-AzureStorageBlob -Container $Container -Context $ctx
# Set tier of all the blobs to Archive
$blob.ICloudBlob.SetStandardBlobTier("Cool")