I am using an updated iPhone 4s 6.1 and this is how I jailbroke it using Evasi0n on Windows 8.
Prerequisites
This is fairly simple
- Install iTunes
- Make sure your iPhone is updated to 6.1
- Backup your iPhone if needed
- Run Evasi0n
- Wait until you iPhone is recognized
- Select Jailbreak
- Wait a couple of minutes for the program to do its work (The iPhone will restart, be patient)
- it will ask you to unlock your device and click the new jailbreak icon (look for it)
- it will finish up and do a couple of restarts
That is it, your iPhone reboots with cydia installed