This is the link I used. It downloads the kobo software, not the useless borders app we know and love...
You don't actually need to log on to the kobo app for the firmware upgrade, which is good. Have a look at a few other threads here for any potential pitfalls.
The upgrade fixes the font scaling and a few other things, but does introduce an autopowerdown function which many people (including me) find extremely annoying. Your call!