unable to install version 2.0

[Tom Swan]

I copied and executed script "lilypond-2.20.0-1.linux-64.sh" from the Downloads page. It seems to run but afterwards, "lilypond --version" still reports GNU LilyPond 2.18.2. What am I doing wrong? Also tried apt-get upgrade lilypond, which reports  "lilypond is already the newest version (2.18.2-12build1)" so now I'm stuck. How do I get the newest release?