As far as I know, there isn't a way to edit them directly, so you will have to create a fork and edit that. To do that click the Fork button at the top, which will create your own clone of the repo that is editable by you. once you've made and committed the edits to your fork, click the "pull request" button and fill out some info on the changes. The people in charge should see that and if they like your edits, will merge it into the main repo.