You need to:
1. Have another SD card (8GB for Linux, 2GB for Android).
2. Have card reader in your PC (can be cheap USB card reader).
3. Download Win32DiskImager application.
4. Download new image:
a) For Android:
https://www.dropbox.com/s/wtl9oshdxq..._Kobo_Touch.7z
b) For Linux:
https://www.mobileread.com/forums/sho...d.php?t=220350
5. Write it to your SD card using Win32DiskImager.
6. Open your Kobo's back cover and replace SD card. There are no screws.
That's all. If something goes wrong, you can replace SD card to original one. For safety reasons don't ever write images to the original SD card.
The Linux is much harder to configure and use. You need to install gargoyle (adventure games interpreter) with "sudo apt-get install gargoyle" command from terminal.
I suggest to try Android version. The nice interpreter for Android is this one:
https://play.google.com/store/apps/d...dglk.hunkypunk
but there are others.
[EDIT] My images may or may not work on N905B model. I have tested them on N905C model.