updating XT1092 4.4.4 to 5.1 and root ?

Hi guys,
I have some questions about updating my new XT1092 :
I'm french and have a 4.4.4 android stock version deutsch (21.21.45.victara_retde.retdeall.en.DE retde)
I haven't made modifications (bootloader not unlocked) or update to keep maximum root possiblilites.
i want 2 things : update to lollipop 5.1 and root my phone.
But after reading some posts and brick problems, i don't know where to start :
does i need to update to 5.1 first and root after ?
or root first on 4.4.4 version and update to 5 and 5.1 ?
OTA update or manual update ?

Thanks!