Wikis are, in general, extremely open and relaxed communities. In almost all situations, it is considered not only appropriate but desirable for members to correct inaccuracies, update information, expand on shoddy bits and even trim and reformat the crufty bits. Feel free to edit nodes, even if you weren't their creator, so long as you are making it better in the process.
If you see a node that really needs to be updated, and either do not have the time or knowledge to do it, or the confidence that you are the one to do it, simply ensure that it is annotated at the end with a maintenance tag. Usually, a Needs Revision tag is enough to get the ball rolling.
The only node that you really should be careful about are personal nodes. Personal nodes are usually tagged with the following at the end of the content:
This is a {personal node}
When in doubt, the following rule should be your guide: Leave the wiki better than you found it, today.
This node is a part of the Cloud Wiki manual, and was strongly influenced by The Open Guide's Wiki Etiquette.