Before installing plugins or making any major changes to your WordPress site, it's always a good idea to back it up.
Here are a couple useful SEO plugins.
This plugin will allow you to optimize your site's main title, head section, secondary title, secondary description, paged comments, duplicate content, and more.
This plugin allows you to optimize your post titles, meta descriptions, robots configuration, canonical, breadcrumbs, permalink cleanup, XML sitemaps, RSS enhancements, .htaccess, API docs, head section, and more.