Can't detach disk from Centos VM to resize it.

Hello,

I'm fairly new to Azure, but I don't think my issue is my lack of knowledge.

I've created a Centos VM from the quick create options, which gives me a 30GB disk. I need it bigger. I couldn't see an option to create a bigger disk anywhere on the create section, even on the gallery.

So now I want to make my disk bigger. I think I can just detach it, expand it and attach it again. Except I can't detach it.

In my machine dashboard, the icon to detach isn't selectable. I can attach more disks, but not detach.

Am I doing something wrong?

Thanks,

David