There's no need for a guide for such simple a matter. First of all, to update your PS3 to the latest firmware it's always better (and safer) to update through the computer (via USB). Visit the official PlayStation website and, if they ask you which region, select North America. After you're redirected to the North American PS page, scroll down to the bottom and on your right you'll see a banner with a large '3.50' written on it. Click on it. After that, click on 'Download Now' in the page you're taken to. From there, just follow the instructions and the update is as good as yours! In the USB, make sure to create a folder named PS3 and then create another folder inside the one you just created named UPDATE (in all capitals). Put the update in the UPDATE folder.