How to allocate more space to my root partition?

I've a macbook running with snow leopard. I 've recently installed LTS 16.04 on dual boot.
In the last few days hoverer, I have been not able to manage this system because I do not have any root
space at all. So, how to allocate more space to my root folder?

Many thanks in advance

Aldo

Bildschirmfoto vom 2016-08-09 06-20-48.png

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