The version of Audacity in Ubuntu (Audacity 2.1.2) lags behind the current release version of Audacity (2.2.1).
Features that have been added to recent versions of Audacity will become available in Ubuntu when they catch up.
If you want to use the current release version of Audacity, the recommended way to get it is to build Audacity from the source code.
I posted a (slightly out of date) step-by-step guide for that here: Building Audacity 2.2.0 on Ubuntu 17.04 (Zesty)
Alternatively, more recent versions of Audacity may be available through PPAs.
“Panda Jim’s” PPA is not an official release, but he generally keeps it up to date: Audacity Audio Editor and Recorder : Panda Jim
Note that you should only install software from sources that you trust.
I would strongly encourage users of PPAs to ensure that they understand the risks of using PPAs, and know how to cleanly remove a PPA (and any software that they have installed from that PPA) before they use the PPA.