Can I Update iPhone 4 to iOS 9?

The answer to that question is a resounding yes. Before starting the upgrade, ensure your iPhone 4 is backed up on include or computer through iTunes before carrying out the update.
Then carry out the following steps:
Step 1: Backup is a preliminary step. This is done to ensure that you do not lose data which has changed since your last backup. It is also really hard to start from a scratch.
Make sure you reinstall apps, add email accounts and also sync in contacts and enter passwords and logins.
Step 2: Make a complete backup to iTunes and start the encrypt backup box
Remember that your passwords and apps need to be backed up and restored in case there is a requirement for the same.
Step 3: Make sure your device is authorized to sign in to back up all your apps
Step 4: It is not needed to back up all the apps, as they will be automatically downloading at the point of a restore. 5GB of free iCloud storage is not enough for complete backups.
Therefore, you need to pay for extra storage if you don’t want back up through iTunes
Step 5: Check the space available by tapping Settings followed by General and Usage. List of applications will inform you which ones are using up the phone or tablet storage. Photos app will be filled with snaps and videos for example.
Step 6: You can transfer photos, videos and songs to PC or cloud using the following services:
Dropbox
Google Photos
Other such
Videos use up most space but these should not be backed to the iCloud Photo stream
Step 7: The final step is quite simple. You need to download iOS 9 on your iPhone 4 and install it following onscreen instructions.
While iPhone 4 can be updated to iOS 9, it is not recommended that much. This is because iOS 9 tends to slow down the particular model of the iPhone. Troubleshooting is also difficult because the original iPhone 4 was not meant for an update to iOS 9. Apple products are generally superior when it comes to use and efficiency. But bear in mind that if your iPhone is the apple of your eye, you need to make sure it does not malfunction. Upgrading to iOS 9 could play a huge role in this. While you can technically update the OS, experts caution against it.
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