Open spine.exr in Photoshop. If your version is too old, it may not support EXR files and you will need to upgrade. I am using version CS2. This should bring up a window that looks like:
Obviously this could stand to look more lightning-like, so go to Image->Adjustments->Exposure.... Or, if you want to ultimately export your results to a low dynamic range format (such as GIF or JPG), go to Image->Mode->8 Bits/Channel, and it will bring up more or less the same sliders as the Exposure... menu.
There should be at least two sliders, Gamma and Exposure. A good rule of thumb is that Exposure controls the thickness of the central bolt, while Gamma controls how much glow the secondary side branches have. Adjust these settings until you obtain the desired result. An exposure adjusted version of spine.exr is shown below:
After setting the exposure, you can tweak the final color of the lightning by going to Image->Adjustments->Color Balance... and using the color sliders. The previous image after color tweaking is shown below:
> Go to render tweaking
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