iOS 8.1.1 Firmware

Here are the links which support to your devices. Unfortunately, the iPhone 4 doesn't release the iOS 8. But you can enjoy others:

iPad Air 2 (6th generation WiF)

iPad Air 2 (6th generation Cellular)

iPad Air (5th generation WiFi + Cellular)

iPad Air (5th generation WiFi)

iPad Air (5th generation CDMA)

iPad (4th generation CDMA)

iPad (4th generation GSM)

iPad (4th generation WiFi)

iPad mini (CDMA)

iPad mini (GSM)

iPad mini (WiFi)

iPad mini 2 (WiFi + Cellular)

iPad mini 2 (WiFi)

iPad mini 2 (CDMA)

iPad mini 3 (China)

iPad mini 3 (WiFi)

iPad mini 3 (Cellular)

iPad 3 Wi-Fi (3rd generation)

iPad 3 Wi-Fi + Cellular (GSM)

iPad 3 Wi-Fi + Cellular (CDMA)

iPad 2 Wi-Fi (Rev A)

iPad 2 Wi-Fi

iPad 2 Wi-Fi + 3G (GSM)

iPad 2 Wi-Fi + 3G (CDMA)

iPhone 5 (CDMA)

iPhone 5 (GSM)

iPhone 5c (CDMA)

iPhone 5c (GSM)

iPhone 5s (CDMA)

iPhone 5s (GSM)

iPhone 6

iPhone 6 Plus

iPhone 4s

iPod touch (5th generation)

With iOS 8.1.1, you can use TaiG to jailbreak easily.
Link of TaiG Jailbreak Tool. Click here.