How do i upgrade ASDF (for Lisp management) from 3.1.7 to 3.3.1?

I receive a Warning message from SBCL informing me that, in this session, I am using ASDF 3.3.1, but that I have ASDF 3.1.7 "registered." I previously had my Emacs (/sbcl/slime/quicklisp) environment set up and working but ran into some issues fighting with my distro's (*Ubuntu 17.10*) package-management system... and completely uninstalled and re-installed. Specifically, I installed the Emacs,SBCL & Quicklisp packages from Canonical's repository. Taking the advice of another who knows more about these things than I, I installed Slime using **gnuELPA** from within Emacs. I have no knowledge of which package is responsible for the **ASDF 3.1.7**, nor how I ended up (from SBCL's viewpoint) with **ASDF 3.3.1**. I would like for my environment to be consistent and remove the warning message. I don't notice (because I'm still learning Emacs & SBCL, perhaps?) that this is causing me any other issues. My question, frankly, is: **How do I upgrade SBCL from 3.1.7 to the latest (presumably 3.3.1) version?** I don't yet understand what this is trying to tell me: > (a) upgrade this configured ASDF to a newer version, > (b) install a newer ASDF and register it in front of the former in your > configuration, or > (c) uninstall or unregister this and any other old version of ASDF from > your configuration. because ASDF installation is apparently transparent. I don't recall installing ASDF directly. The last line of the warning message is clear: RTFM and/or seek an expert. I've begun the reading part... and, expect it to take a fair amount of time. If any expert would like to share their gray matter with me, I'll much appreciate it and provide any further details that may be necessary for the solution I seek.