Okay so I was using windows 10 prior to switching to Kali Linux. I have a 500GB hard drive out of which I gave 70GB to Linux. I dual booted Linux with Windows 10.
So now I wanted to completely delete Windows 10 and give all of my drive space to Linux. I deleted the two partitions I had on Windows using gparted. Now I have about 397GB of unallocated space. But I can't extend the partition in which I have Linux installed because the unallocated space doesn't show up there.
And one more thing. I have unmounted the partition in which I have Linux installed I booted the live ISO on flash drive and now I am in live session.
Here are the screen shots.