Need help with my Facebook page can't change Page Info?

[confused composing]

Then try this. After you open your About, click on the "x" that appear on the right of Edit on the relevant data that you want to change, a pop-up will appear, there's a button (at the bottom) to remove that data, click that then Save, the data is removed.
After that, you can put your new data as usual.

(Edit button used to edit/add further detail data.)