It's really not hard, so I can't really fathom why no one has done it!!!
Most important roles (EMO, LGBTQ, Welfare, etc...) should already have accounts on the website. These will have the correct permissions needed to edit pages. Just visit the page you wish to edit and click the great big edit button!
It can of course happens that you do not yet have the required permissions in which case please contact me, jcr.webmaster@balliol.ox.ac.uk.
You may wish to note the above!