Click on a cover.
Click your current status:
Now click on the status you want to make inactive (take back, undo.... whatever you want to call it)
Now you have a clean slate and can choose any status you want:
So let's make a DNF status:
And then you save.
Or you can add statuses on your shelf view (this one works for sure, I've tried):
You can give a book more than one status:
Or just one. Than after saving it looks like that:
*not shouting ;)*