First of all, upgrade your iyunes to the lates version, then restart your computer. Upgrade your phone iOS to the latest version using iTunes, when that one is done, get
redsnow for windows or for Mac from here scroll down/middle of the page and you will see the download links there. That's the official website.
Get the ipsw iTunes downloaded to upgrade your phone to the latest version at this location in your computer:
You should first allow hidden file to be showed, you can clic organize >folder and search options. in the popup wondow clic on tab "view" then mark "show hidden files, folders and drives" when that's done go to
C: user > username(your comp user name) > appData > Roaming > apple computer > iTunes > iPhone Softwarw Updates. In that folder you will find your the ipsw which was downloaded by itunes and used by itunes to upgrade your iOS. you can copy, NOT CUT the ipsw to another location like to your desktop. When you start redsnow and it arrive to step 2 browse to your desktop and find the ipsw there.
On a mac computer :
Home Folder/Library/Application Support/iTunes/iPod Firmware
Run redsnow and when ask to locate the ipsw, find it from your desktop. Follow redsnow onscreen instructions to jailbreak, once the jailbreak is done you will either use your gevey to unlock or buy a new gevey. I'm not sure about gevey and I don't know how it works.