How remove alpha channel from PNG image?

[depler]

When converting image from PNG to JPEG transparent pixels are filled with black. How to replace this color to custom or remove alpha channel completely?

[depler]

Got it, in case if someone interested:

using var image = Image.Load("path/to/file.png");
image.Mutate(x => x.BackgroundColor(Color.Red));
image.SaveAsJpeg("path/to/file.jpg");