This SEO plugin checks the content of posts/pages for the keyword density (single/phrases) while writing and is automatically setting the META-tags.
keyword-statisticsfolder to the plugins directory of your blog.
Updating: If you are updating by uploading the files by your ftp program you should login as admin after it. This way options added in later versions will be initialized without changing the way your blog has served meta informations before.
After updating you should check the plugins configuration at the options panel and save the settings. If anything goes wrong with the plugin do this first. There may are new options for whom an initialization is needed and this will be done by saving the configuration.
Just tell your authors which keyword density you need and let them create the content - the on-page SEO work will be done automatically. Remember that all META informations (meta keywords, meta description and the meta-tags for robots - and moreover the canonical url in WordPress versions less than 2.9) will only be generated and served by your blog if you have created or edited your posts or pages after installation of the plugin. Each older post or page has to be opened and saved manually if the keywords, description and robots META should be generated (if you configured automatic setting of meta data) automatically. After that the header tags for search engines will be set and served from the next page-request on. By the way you can check the keyword density of the page content - maybe you have to change the text a little bit to reach your desired density.