
Apple finally took the curtain down from around its impressive iOS 8.3 update and it has been available for iOS 8 users around the globe. You can learn about the changes and features from Apple’s website. Are you still straddling the fence about whether to update your iPhone 6 Plus to iOS 8.3? You need to have a try and then decide whether it is as worthy as you expect. Make sure that you have backed up everything important thing up. Then, what is the best way, you may wonder, to backup your iPhone 6 Plus before the updating?
Generally, there are three ways to back up data on your iPhone 6 Plus.
Solution 1: You can sync your iPhone 6 Plus to iTunes.
Get your iPhone 6 Plus connected to your computer and then run the iTunes (make sure you are running the latest version).Tap on Backup now at the right bottom under the title of Manually Back Up and Restore column. You can locate your backup file by following the route below:
\Users\(username)\AppData\Roaming\Apple Computer\MobileSync\Backup\
To quickly access the Application Data folder:
In Windows Vista or Windows 7: Click Start.
In Windows 8: Click the magnifying class in the upper-right corner.
In the search bar, type:%appdata%
Press Return.
Double-click these folders: Apple Computer > MobileSync > Backup.
If you are using Mac, you can locate the backup file by going to ~/Library/Application Support/MobileSync/Backup/
As you can see, iTunes back up everything on your computer, and thus the storage depends on your Mac or PC's available space.

Solution 2: You can back up your iPhone 6 Plus to iCloud.
You don’t need to plug your device into a computer or even be at home to make a backup with iCloud. The wifi connection, however, is a must.
Connect your device to a Wi-Fi network>Tap Settings > iCloud > Backup.
Make sure that iCloud Backup is turned on.
Tap Back Up Now. Stay connected to your Wi-Fi network until the process completes.
Make sure the backup finished by tapping Settings > iCloud > Storage > Manage Storage. The backup you just made should appear with the correct date and backup size.
Comparing to iTunes backup, iCloud offers up to 1TB storage and the first 5 GB is free.

Solution3: Back up your iPhone 6 Plus to your PC or Mac
Extract important data including Contacts, Notes, Calendars, Reminders, Messages, Messages Attachments, Safari Bookmarks, Voice Memos, Photos and etc and transfer to your PC or Mac for a physical backup. You can directly extract the data from your iPhone 6 Plus by getting your iPhone plugged in to your computer. To achieve this, you need to install the third party software, iFonebox is a great choice. As professional iOS data recovery software, it is capable of recovering and extracting various data from iOS device like iPhone, iPad and iPod Touch as well from iTunes/iCloud backup files and transfer to PC or Mac.

Extract the data from iPhone 6 Plus and transfer to PC is just as easy as a couple clicks.
First, install and run full version of iFonebox, and then get your iPhone 6 Plus connected to your computer.
Second, choose whatever data you would like to extract by tapping on the related icon, or you can check “Recover All” to extract all the data that iFonebox supports.
Third, Preview and transfer to PC for backup
You can do some modifications to the data before transferring to your computer.
I must say, iFonebox is not perfect because it does not support apps backup, but I have to admit that iFonebox makes backing up and transferring data selectively possible. That is iTunes/iCloud could not achieve. And the fatal defect of iTunes/iCloud backup is that existing data will be overwritten and erased forever when you choose to restore from iTunes/iCloud backup file.
So, my conclusion is to combine solutions above to work out the best one. You can firstly extract the data that iFonebox (mostly are important and editable data) supports and transfer to your PC and then delete them after the backup file. And then choose to sync your light-equipped iPhone 6 Plus to iTunes/ iCloud. In this way, you can make much available space for the iOS 8.3 update as well as free yourself of worrying about data overwriting.