So if you are one of this idevices :
and you are using ios 7.1.1 and you don't want to upgrade to ios 8 to lose your jailbreak data
so go a head and upgrade to ios 7.1.2 after the time is go.
and if you don't care by the jailbreak and you want to upgrade to ios 8 what you will need is to backup all your necessary data and apps with your pc or mac
then you can now to get started with new ios 8...