The truth is that you can do this with any web browser & any editor, on any platform. For typos and little corrections, that's more than enough. But for complex changes, or to drill down in a complicated web page and look at the CSS, there's a better way.
- Get Firefox, still the best web browser in the world.
- Install the Firebug add-on, the fastest, simplest way to drill down into a web page and make the changes you want. And,
- Find the email of the web page's author or owner.
... and email them the changes. If it's as small as a typo, you don't even need to do that; just mail the change, with the disclaimer at the end.
And if you're a web developer or site admin, consider applying it. And thank you for helping us make the web better.