Apple's iOS 9 update now makes it possible to install an ad blocker. This isn't system wide, and will not block ads within apps. It's just for the browser. To do this, you'll have to download one of several ad blocker apps that are available in the App Store. Leo uses Crystal. Then you'll see in the settings that you'll be able to enable it.
This is a controversial decision because on one hand, ads have become egregious and take up the whole screen or use a lot of bandwidth. There's also security implications because many ads use technologies that could allow malware, although this issue is more relevant to desktops. In many cases, advertisers are tracking you as well, and ad blockers will block that tracking.
However, it eliminates a source of revenue for most websites. So when you go to a website and see ads, that's what's paying for that site. By not seeing the ads, the site won't be able to make money to operate. As someone who's made his whole life on advertising, Leo is sympathetic to those who depend on ads. But Leo also understands that ads are really out of control, and can actually cause problems for people.