The only reason people install LTSC is to not upgrade to a new build every 18 months (Home/Pro) or 30 months (Edu/Enterprise).. You are up-to-date with the officially chopped LTSC edition of version 1809. There is nothing to upgrade to until the next LTSC release. And when that comes, you need to do it via ISO image, it won't be offered via Windows Update or Update Assistant tool. If you just want to leave LTSC behind, get a business ISO, mount it, and setup Enterprise 1909 / 2004.