Post Metadata Editor

Sorry if I post this under the wrong subforum, but I’ve been trying to find a plugin for changing post metadata (not sure if this is how you WP devs call it) and I haven’t been able to find anything. Maybe this could be done without the aid of a plugin.

Basically what I mean to do is to be able to change the “metadata fields” in each post, so I could either remove the standard ones or add new fields. By metadata I mean the info that’s attached to the post (depends on the theme, on the one I currently use it’s displayed on the left of the post, while on other themes it’s placed at the bottom) in which the date, categories and the tags are shown.