How do i delete unused disk after restoring an image?

I had to restore a saved image to my Linode, but now that I've gotten everything fixed I can't create a new image of its current state. I believe this is because the original disk which is not being used is still there and this is causing me to be above the 6GB limit for images.

I found this old question which I believe describes my issue - https://www.linode.com/community/questions/17841/do-restored-linodes-take-up-extra-hd-space

But I don't have anything that says "Advanced Configurations" in my Linode settings as described in the solution to that post. Has it been moved or am I missing something? Thank you.