Why disk space is not released after deleting virtual disk

Why disk space is not released after deleting virtual disk

I installed ubuntu via wubi with the size of 20Gbs. Then i decided to
increase it to 65 Gbs using this guide.
Then i decided to delete this virtual disk (65 Gbs) to increase to about
150Gbs. The only thing i didn't follow the guide is that i delete this
virtual disk from ubuntu using rm command (The guide seems mentioned to
delete it from windows in the last step)
After removing this virtual disk, i see the free disk space remained the
same (not increased 65 Gbs as expected).
Anyone know how to fix this, so that i can have 65 Gbs free space back?
Thank you very much