I have successfully extended internal memory of my Kobo GLO with a PNY micro SD / 32 Go, class 6. On the Glo there is no screw at all. Just carefully remove the back cover (not easy but possible with force and patience).
It may be obvious
but the drive must be UNMOUNTED for gparted to work on it (if not, all right-clic options are greyed out).
I did a reset (not "reset to factory" option but with the little hole next to the usb port) and all is normal (before that the Kobo was not very responsive).
Total storage memory now : 29759 MB. Whoo
This thread deserve to be sticky.