

Copy the downloaded file in to the resourcepacks folder that Minecraft just opened.

Switch away from Minecraft to your desktop (if it didn't automatically).If you want a different green than the one I picked and have some facility with zip-file creation and image editing software, you can find the one texture file it contains and change the triangle of green to a green more to your liking. Since googling turned up nothing except broken links, I threw one together: Green Grass Texture Pack Texture packs like that used to be popular due to nostalgia for the grass in older versions of Minecraft, but my googling just now reveals that they're a harder to find now. The difference in colours is controlled by one texture file though, so it's easy enough to fix by installing a resource/texture pack that changes that file to be one uniform green instead of a gradient of greens and yellows. Grass is different colours in different biomes, and you're seeing the "dry desert" grass colour in the middle of your screenshot.
