I have changed the vdi size from 20 GB to 40 GB, but the increase has no effect on my ubuntu machine, it still says the memory is as it was earlier. Two screen shots have been provided, the host is windows 7 professional, the guest is ubuntu 14.04 LTS, the virtual machine is oracle vm virtualbox.
the screen shot is of storage of virtual machine settings
the output of df -H command in ubuntu terminal
The question is how I can have the effect of resizing vdi on ubuntu machine.