A Content Management System (CMS) is used so that an untrained person is only allowed to make edits in certain places.
Two CMSs are frequently mentioned on this board:-
Joomla has a lot of capablities http://www.joomla.org/
Snippetedit http://www.snippetedit.com/ is for simple edits of text or images. There is a demo. If you allow someone to upload images, they may upload images too big or small and wreck your layout unless you put in sizes in the code like
<img style="width: 300px; height: 100px;" src="image.jpg" alt-"Image decscription">
and only allow the image filename to be edited which should resize any uploaded images. Also cancel the image sizes in the Snippetedit upload menu.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.