Azure disk management is not smooth and easy.
To resize your sys disk no other solution than delete the vm with retain disk .
Resize with the tool after deleting the disk from "vm" but keep data in the blob.
After resize you have to add a vm with an existing disk .
Remember to save vm name , disk name , acl in firewall etc .
Last resize of an old azure vm i used this blog post : http://blogs.lessthandot.com/index.php/enterprisedev/cloud/azure/expanding-an-existing-azure-vm-system-drive/
There is a new solution with cloud explorer but i never tested (and you have to delete the vm like the first one methods).
And i don't explain how to expand ubuntu lvm because there is already many blog about that :
( http://www.linuxuser.co.uk/features/resize-your-disks-on-the-fly-with-lvm)