October Guest OS rollout is starting today October 15 2015, and projected to be released on November 13 2015.
Azure Guest OS Releases and SDK Compatibility Matrix
https://azure.microsoft.com/en-us/documentation/articles/cloud-services-guestos-update-matrix/
In the meantime you could read the below blog post manually install .NET Framework 4.5.2 on a cloud service.
https://azure.microsoft.com/en-us/documentation/articles/cloud-services-dotnet-install-dotnet/