How to jailbreak iphone 4 free?

I'm trying to jailbreak my phone 4.

It depends on the firmware version it's on. Redsn0w should cover most firmware versions though. Get it from the dev-team's blog.

Okay if you want to jailbreak that's great but remember the consequences. Okay I recommend you use redsn0w or greenpoison although redsnow is better or even absinthe. Remember the beta version of the type of file you are going to use to jailbreak such as redsnow 0.9.12 beta 2 for my ipod touch 3. You could find that on the web. Type in your ios version and type in the type of file you are going to use to jailbreak which would be redsnow in my case. Plug in the device after it recognizes the device then hit jailbreak. And for redsnow it will use rocky racoon 5.1.1 you can check more on youtube if you want.

What's your firmware? You can find free step-by-step tutorial here http://iphone.pandaapp.com/jailbreak/