Increasing the internal storage of your eReader is the same as replacing it up to this point.

The rest of this guide is only relevant if you use an SD card with more capacity than the original one.

I also strongly recommend Linux for this. I used Linux Mint, but any modern distro will work.

You might be able to do this with some homebrew tools on macOS or WSL on Windows, but I haven't tested that.

In some screenshots I'm using a 512GB SD Card and and in others one with 32GB. That's because I had to go back and take more screenshots.