Hi
If this allows at least one person to avoid some of my mistakes, it will serve its purpose.
Upgrading Glo
I tried to upgrade from 2.5.1. to 2.8.1. I thought it was an elementary task.
- Using "sync" only managed to perfect - after a long time using Wifi - my 2.5.1. firmware.
- After that, I reinitialized my Glo (long press + light button press), it wiped all my books, took me quite a long time to finally land in 2.6.1.
- This time, I looked for information, downloaded the 2.8.1. firmware, side-loaded it in .kobo folder (upgrade + manifest + koboroot) and finally got it working.
Morals 
1. R.T.F.M. (the wiki is OK too...)
2. Save everything before, you never know