Older Kobo

I still have an older model Kobo ereader (and a new one - but the old one won't die!). It has outlasted several later ereaders of different types and still soldiers on, being used as a spare. Originally this model was connected to the Google Book store until some years ago when Kobo set up their own online store.
My question is - is there any way of connecting to the Kobo store and updating books or is Calibre or Adobe Digital Editions the only way books can now be loaded? I can't imagine there are still a lot of these early models out there!