how to control version of slime in emacs (using melpa package installer)

"Mark H. David" <[email protected]> Tue, 23 Jan 2018 15:57:31 -0800
Newsgroups gmane.lisp.slime.devel
Message-ID <1516751851.2482630.1245877872.55785DAB@webmail.messagingengine.com>
Hi, I installed SLIME with the package installer (melpa), and I have no idea how to control the version. I would like to run version 2.20, but I seem to have version 2.19. Does anyone know how I can change to version 2.20?  I cannot find any documentation about this. Can anyone point this out?
Thanks,
Mark