Can't resize /dev/sda1 on gparted on Ubuntu 14.10 VirtualBox
Solution 1:
Just as in a bare metal system we can also boot our virtual machine from a live CD .iso we had mounted as a CD-ROM to our virtual machine.
Make sure you leave the hard disk boot order allowing to boot from CD-ROM first.
After that we will boot this machine from a live session where we can access the still attached virtual drive from GParted.
Consider taking a snapshot or export your VM before you change partitions.
Also see: How do I increase the hard disk size of the virtual machine??
In case we do not need to increase the partition size of the exisiting partition but only need more space, e.g. for HOME, we can also partition the still unallocated space of our resized hard drive. This new partition can then be used for additional space in the VM.