Smoothing arcs to curves

Is it possible to smooth out arcs into curves once they have been created? I have read one or two articles on the subject, but I can’t make sense of them. Any help would be much appreciated. This is an example of what I am doing.

From my experience, to get the smoothest curves, specify the amount of sides prior to drawing arcs. In the lower right of your screen, there will be a prompt to input the amount of sides, since SU bases arcs and curves on sides. Depending on how complex and precise your curves are, you’ll want to specify 48 or even 96 sides. it helps to keep your amount of sides to even numbers, or divisions of 12 (since 12 is the default, then 12, 24, 48, 96, etc sides will look smoother).

Yes I know that now. This project is near a year old, so I’m loathe to start over. My question though remains, can we smooth out existing geometry?

The simple answer is, No. Sketchup geometry is simple edges and faces and is not parametric.
The more complete answer is, yes depending on what it is and how you want to tackle it. Things like SUbD and Artisan can smooth such things but they will also change the size and shape of the geometry in the whole piece.
If the geometry of the arc you want to change it a simple face you can extend it and draw another arc with more segments.
If it a rolled edge it becomes more difficult… and so and so forth
If you want the whole Panels, the bumper, the wheel arch, to be smoother then you need to do a bit of remodelling.
But if you just want to make the finished edge of the wheel arch smoother you could intersect a smooth cylinder with the arch and the bumper and trim them off, then extend them as necessary.

Much as I thought. It was mainly the wheel arches (and the arc of the side window frames) that showed up greatly on my rendering. Shouldn’t be too hard to fix. Thank you @Box