I would like to add a screen shot of what I'm seeing when trying to edit this particular page, but I'm not susre why I can't add one here.
There are no other areas options showing for me - I have seen them when creating the website a couple of years ago, but the 5 areas options are just not showing.
In theory all pages now always have all the areas available all the time - there's no need to switch to a layout that has fewer slots available.
The columns/slots only appear on pages if there is anything in them, so you essentially choose the number of slots in your layout just by putting things in them or not, rather than changing the layout to hide/remove those slots.
Do you have pages where all the different slots are not showing up? If so please let me know and I'll see what's happened, and enable them all for you.
Thanks
Joe