Help removing radiator cover for cleaning

Hi all,

Looking for a bit of help with our radiator covers as we're having an absolute howler trying to get them off to clean between the fins


Basically at the bottom there appears to be some some of washer or something which means you can't just slide the sides up which is what every YouTube video I've watched seems to suggest!

So, before I lose the plot and rip the thing off the wall, any ideas?
Thanks!