Go to your .minecraft directory (if you don’t know where that is, click the Start button and type %APPDATA% in the search bar, then click on the “.minecraft” folder).
From here, go to the “versions” folder, open any folder inside (for example “1.8”), and open the .jar file inside with a zip archiver program (for example Winrar of 7zip).
From here enter the “assets” folder, and then “minecraft”, “textures”, and finally “painting”.
You’ll find a file called “paintings_kristoffer_zetterstrand.png”. Copy this (or extract it) and paste it anywhere like on the desktop. Open it with an image editing program like GIMP or even MS Paint. You’ll see all the paintings there and you can edit them however you want. You can even increase the resolution of the file.
Now you must archive the modified image file into a new zip file (name it whatever you want) using the same program you used to previously open the .jar file. But this zip file has to have the same folder structure as the .jar file, so you’ll need to put the .png file in a “painting” folder, which needs to be inside a “textures” folder etc. When you open the new zip file you made, the first folder you should see is “assets”.
You’re almost ready but you also need to make a file called “pack.mcmeta”. Open any text editor like the Windows Notepad, and type in the following:
“description”:”name of pack”
Then save the file as pack.mcmeta (not pack.txt). Put this file in the zip file you have just made (so when you open the zip file you should see the “assets” folder and the “pack.mcmeta” file.
Finally, put the zip file in the “resourcepacks” folder in “.minecraft”. Open Minecraft and you should see the resource pack in the Resource Packs menu.