Your screen porch is composed of an aluminum framework with screen inserts. It can be dismantled, though it follows that the corner supports are holding up the roof.

The only way to increase the square footage of the screen porch is to demo it completely and start over. Do you really want to undertake all of that? It's going to affect your siding and roof. $$$$$

Looks like you could extend it in one direction.

Removing the screens and railings and not replacing them? I’m sure you’ve heard people say they’d love a screened porch - why are you removing yours?

I think we need a bit more info please. I could see opening one wall and building a deck to match the height and making that space a place for the BBQ but then the whole point of the screened in porch is lost .So then you might just as well remove all the screen and railing except for the corner post . Please give us a bit more to go on.