to my knowledge you'll want to go to https://sickchill.github.io/ and download the appropriate version for the operating system your current sickchill is running on. it should be a matter of just overwriting your current sickchill files with the new ones from the site. you shouldn't need to back up anything since it won't be overwriting your config or your show database.
You might also think about SickChill at https://sickchill.github.io/
There's going to be a lot of change between Sickbeard and Sonarr. Not that I'm saying it shouldn't be done, because Sonarr is awesome. But if this is already too much, then SickChill is a currently-maintained fork of Sickbeard.