Resize VDI with
File > Virtual Media Manager. If you are using snapshots, remember to resize all snapshots.
Reference: resize vbox disk.vhd with snapshots | SpiceWorks.
Resize with GParted Live CD.
If you are using LVM, run:
df -h # view volume path lvextend -l +100%FREE <VOLUME_PATH> resize2fs <VOLUME_PATH>
<VOLUME_PATH>should be something like
The usage of the 2 LVM commands can be found in this post.