How I do it is that I use 7-Zip (
https://www.7-zip.org/) and Paint.net. (
https://www.getpaint.net/). Once both are downloaded, I:
- Go to the windows icon in the bottom left of my computer
- Right click and press "run"
- Type in %appdata% and then enter
- Go into .minecraft
- Go into versions
- Choose what version I want to modify and go into that folder
- Right click the .jar and go to 7-zip
- Find "Extract..."
- Make a folder on my desktop
- Direct the extraction there
- Let it extract
- Go into the new folder and type in ".class" in the searchbar
- Ctrl + a to select all
- Delete all .class files
- Go back to the main folder and delete all of them EXCEPT assets.
- Go into assets and make sure the only folders there remaining are "blockstates, lang, models, particles, texts, and textures."
- Go into textures and open paint.net
- Drag the texture you want to change into PDN
- Press "Open"
- Start texturing!
I hope this helped.