Apple has stopped signing iOS 8.1 meaning there is no way to either upgrade to it, or downgrade to it. Instead, you’ll have to go directly to iOS 8.1.1.
Fortunately,TaiG has released a jailbreak utility for iOS 8.1.1 that works on Windows. iOS 8.1.1 was officially jailbroken. TaiG can be used to jailbreak iPhone, iPad, and iPod touch running iOS 8, iOS 8.0.2, iOS 8.1, and iOS 8.1. It works well and is pretty easy to follow along.
Users who have already been jailbroken on iOS 8.1 can decide whether to stay put on iOS 8.1 or upgrade to iOS 8.1.1. But those who’re not jailbroken and are currently on a non-jailbreakable firmware, have to upgrade to iOS 8.1.1 if they wish to jailbreak now.
You can use the below instructions on how to jailbreak your device.
Step 1: Download the latest version of TaiG jailbreak on your computer, and unzip the zip file. You are also required the latest version of iTunes.
Step 2: Connect your device to your computer using the USB cable.
Step 3: If you have password on your iPhone or iPad, disable it from Settings > Touch ID & Passcode.
Step 4: Turn off Find my iPhone from Settings > iCloud > Find my iPhone.
Step 5: Launch TaiGJBreak as an Administrator. Right click on the TaiG exe and select the “Run as Administrator” option.
Step 6: TaiG will take some time to detect your device. Once done, deselect the TaiG App Store, just below Cydia 1.1.16.
Step 7: Click on the green jailbreak button to proceed:TaiGJBreak will start the jailbreak.
Step 8: After the jailbreak is complete, your device will reboot automatically, and you will see the Cydia icon on the Home screen.
Congratulations, your device is jailbroken!