Log in using the username/password you received in email when your wiki account was created.  You must be a member of a GENI working group mailing list to get an account.  Any [http://lists.geni.net/mailman/listinfo GENI mailing list] with a "-wg" suffix is a working group mailing ilst.

At the bottom of any editable page, you should see the buttons that let you change wiki contents:  "Edit this page," "Attach File," "Delete this version," and "Delete this page."  Once you choose one of these actions, you will get appropriate buttons to carry out the selection, as well as an editing window if you need one.  

Someone else may be editing a page at the same time you are.  If the original page has changed, the wiki will notify you of this when you use the "submit changes" button.  Copy the text you were working on into your browser, look at the changed page, then use the "edit this page" button, paste in your changes, and hit the "submit changes" button.