Installed TeamViewer on one of my computers. Tried to connect. Was informed that the version I am connecting with is 12 while the newly installed computer is 13. No described update procedured worked out. It was referred to an entry in Help pull-down menu named "Check for new version". It is not there in my version:
Debian Jessie, TeamViewer version 12 on client system, Debian Stretch, TeamViewer 13 on server system.