I created a VM using Virtual Box, but I gave it 25 GB, and I had 15 GB free. So I deleted it, and soon, uninstalled Virtual Box, but when I open my filesystem's properties, it is full, I mean to say about 80% of it is still in use, and the vdi file isn't anywhere. How do I free it up?
By default your VirtualBox files should be located in
$HOME/VirtualBox VMs/ so if you navigate there you should easily see if there are any remaining
.vdi files still in place.
If your files were in a non-default location try running the following in a Terminal window to find them:
find $HOME -iname *.vdi
And when you find the files you can manually delete them...