Paint (easy) or take the panels down (might get messy).
Question is: Do you like the panels or would you prefer a straight wall?

Colour?

Taste?

dablin, photos would help get a better feel for the room.

Try doing a white wash over the paneling - I had an apartment years ago that the owners did this as an affordable way to brighten up a dark space. It looked good! Share some pictures if you can.

Yes, just paint it a light color for sure! A sunroom should be bright and refreshing I think!
I have a screened in porch that has 2 walls that are brick. It was a little too dark for me as well. I painted the brick an off white and painted the trim in a light khaki color and painted the ceiling pale blue. It looks great.

Here is basically what it looks like....We added the ceiling beams and I still have to put a wash over those to look more like driftwood, but it's too cold right now. That will be a spring chore. I also added white curtains that are always drawn over the screened in walls. Brightened it up too. But I have a beachy theme going on, that may not be what you are after.