The paragraph that refers to the style system you're using really has no bearing on how to edit an entry in a community. What really matters is the style system that the *community* is using (unless you're using style=mine).
See the FAQ for what it is currently.
All users can edit entries at http://www.livejournal.com/editjournal.bml. This page allows you to choose an entry to edit either from the most recent entries or from a specific date. To retrieve a community's entries rather than your own, you will need to enter the community's username in the "In community" text box.
Additionally, you may be able to go to the "Post Comments" or "Read Comments" page for the entry you want to edit or delete. You can get to these pages by clicking on the entry's comment links if comments are enabled, or by using the Calendar view (http://www.livejournal.com/support/faqbrowse.bml?faqid=70). On a small blue toolbar near the top of the page, if you're logged in, you should see an Edit Entry button (a blue pencil icon). Click it to go to the Edit Journal Entry page. There you can make the changes you want. Click "Save Journal Entry" to save your changes or "Delete Entry" to remove the entry entirely.