If you're interested, I replaced my 16 GB microSD card with a 64 GB card about a month ago under Arch Linux:
- remove the old card from the GloHD and put it in a card reader
- connect the card reader to your Linux PC but don't mount the card
- use 'dd' to clone everything from the old to the new one (I first wrote everything to an image file I could later use as backup but that's not necessary)
- use a partition manager (KDE partition manager or gparted will work - or just use the available command line tools directly) to increase the size of the user partition (3rd partition) on the new card (I actually first moved the existing user partition a little to the end to make room for increasing the system (1st) and backup (2nd) partition to 1 GB each first before I increased the user partition)
- put the new card in your GloHD and switch in on - it should now boot and you can use it for reading, however:
- at this moment, when you connect your GloHD to a computer the user partition might not be seen as external storage (Kobo's own partitioning is a little non-standard and doesn't necessarily survive the re-partitioning), so, if this is the case,
- go into the setting menu and initiate a factory reset (this will restore Kobo's special partitioning but not actually resize the partitions again)
- after the reboot, make sure, that everything works (if you don't want to go through the registration process, you can switch off the GloHD remove the new card again and put it in a card reader and copy everything from the old to the new user partition - this will save you the effort to set up everything again - apart of course from modifications that live in the system partition (KSM, KFmon, fmon, nightmode, etc.), these will have to be installed again - and then put the card back in the GloHD).