Hey don't worry it might take some time (it all depends on how much free space was there on your phone, on my Lumia 920 8GB was left and gears took 45min to complete) Just keep it plugged in to a power source and it will move after some time. After this step it will migrate your data (19 steps ) and the 13th step might take some time
Oh that's quite long ! I guess then I'd remove all apps which don't have any meaningful app data (eg save files) before upgrading. I'm gonna do a hard reset anyway after upgrading and backing up my save data of games, so i better remove apps for which i dont have any saves.
sorry for off topic, but i need a quick reply:
How does the app data backup work ? For example, if i backup app data of rabbids big bang, would it backup the whole game or just its 'app data', which is shown as a light blue bar in storage check ? I hope its the latter. Also, can i choose which apps to backup and which not to ?