Adjusting the lightness of an image

[Arcanine]

Attached is the image I want to edit.

As you can see, the image is darker around the edge and lighter in the center. I want to make the entire image light like it is in the center. I know about the Lightness setting, but that makes affects the entire image when I use it. I basically just want to make those darker sections lighter, so that it's all the same level. Anyone know how I can do this?

I'm using Photoshop CS5 on Mac.

 

[Hoogle]

You could try going to image > adjustments > shadow highlights
Or using a brush set to lighten mode and paint over it however you will end up with blotchy effects you will be better of recreating the pattern

 

[Stric9]

You may try selecting a color like the center. Solid color fill. Change to luminosity blend mode. Then use blend if to expose only the grid.

 

[Furio]

Use Filter / lens Correction and use the custom setting, change vertical perspective first, followed by a vignette correction.

What's left are stains on the surface that have different light reflection properties. These are harder to fix.

If you have the skills, consider to make a pattern instead.