1. Preparation

Since the iOS9

beta version is also a development preview version, the iOS9 upgrade firmware file cannot be obtained through system update. Download the iOS9 The download address can only be found by logging in with a developer account.

Although the upgrade package is compressed to 1.3GB, you still need to use download software to speed up.

Also due to the instability of the development version, unknown errors may occur, etc. It is recommended that you back up your phone to a computer before upgrading to iOS9. If something goes wrong, you can still use system recovery.

2. How to upgrade iPhone 4s to iOS 9

After the above preparations have been completed, keep the phone connected to the computer, hold down the Shift key and click Restore.

This restore browsing is not the backup file of the phone, but browsing and selecting the upgraded firmware of iOS9.

A pop-up option prompts that recovery will erase all data on the phone. Click Restore to proceed to the next step.

There are requirements for the firmware version to be flashed. When downloading the firmware, it should be consistent with the model of the mobile phone, otherwise there will be a mismatch and the system upgrade will fail.

When the firmware you flash meets the model requirements, the firmware will be verified online. After passing the verification, the firmware will be flashed into the phone. During this period, the phone will restart about three times to complete the system upgrade.