How to Jailbreak an iPhone 4 I.O.S 4.2.1 With Greenpoison

Have an iPhone 4 that you want to jailbreak with Greenpoison? Here's the guide for you.
Steps : 

1. Unzip the archive gp_win_rc5_b2.zip

2.Connect the iPhone and switch off it.

3.Click Prepare to jailbreak DFU.

4.Follow the procedure:-Press 2 seconds on the button Power. 

5.Then without releasing(leaving) the button to power, maintain the button home during 10 seconds.-Then relaunch the button Power and remain press on the button home during 15 seconds.

6.If the Ready to jailbreak message appears, then click to Jailbreak

7.The jailbreak start, the screen becomes quite white 2 seconds then writings on a black background appear.

8.Click Quit at the end.

9.When the menu of the iPhone reappears, look for the Loader application and install Cydia