How do I change my skin color (Photoshop) without Photoshop?

My question is whether there's a good free Photoshop alternative that can easily and quickly change the color of a skin? Eg. Blue → Red

Try it on http://planetminecraft.com/pmcskin3d/

Paint.net is a good image editing software that can be used for many other things. Completely free and all the necessary functions.

If it's something simple, you can also go online via Photopea. Select the Hue / Saturation setting level and then the color range and change the color using the sliders.