Radar and Sonarr are tools to track movies and TV shows respectively. You can add a movie/show to track, tell it the quality you want it in, and set up Prowlarr or Jackett to give Son/Radarr the access to the torrent trackers it needs. You can also use Usenet but I have no experience there.

It will search those torrent trackers for releases matching your movies/shows in the quality and language you set for them and send the downloads to the torrent client you set up. When the client finishes downloading, Son/Radarr copies (or hardlinks) the files to your library folders.

If Son/Radarr is tracking a show that you currently have downloaded in 480p, but the quality profile allows upgrades up to 1080p, it will search for 720p and 1080p releases and pick the best match it can find. When the torrent client finishes downloading it, Son/Radarr will automatically replace the 480p release with the 1080p release it just downloaded.