Wall Vent Advice

Hi,

I have an internally fitted wall vent on a wall where I'd like to install a vertical radiator - see attached photos. Ideally, I'd like to cover the vent with the radiator but the existing vent sticks out quite a bit.

I've tried to remove the vent but it feels pretty stuck. I live in a flat so can't access the vent from outside.

What I'd like to know:

1. How do I remove the vent?
2. Should I replace it with a flat cover that will sit more flush with the wall? Will this be okay with a radiator in front?
3. or should I block up the hole?

I'd appreciate any advice!