Before jumping into the options, are you familiar with Git? If yes, then skip this paragraph. If no, please complete this short course.
You can navigate to the page you would like to edit, click on the Edit pencil icon on the top right of the page.
If you have not been added as a contributor to the website yet, your changes will become a pull request. A moderator will check the pull request and commit your changes if all is good. If you are already a contributor, you can commit your changes and the website will update automatically.
The other option is to clone this repo and edit the website on your local computer first. This way you can check if everything looks good before committing / submitting a pull request.
Then submit an issue here.