sudo /etc/init.d/postgresql restart (how to chose which installation?)

Solution 1:

If you are using debian, you can tell the init script, which version(s) you want to manage:

pg01:~# /etc/init.d/postgresql       
Usage: /etc/init.d/postgresql {start|stop|restart|reload|force-reload|status} [version ..]
pg01:~#

Solution 2:

First, are you running two side by side intentionally or did you just install 9.2 from a different package and it did not remove 9.1? (Postgres packages are now often set up that way.) If you've migrated, then 9.1 should be removed.

If you need both, then each should have its own pg_ctl executable which can do the same thing as the normal initscript. Run it as the 'postgres' user. See .../path/bin/pg_ctl --help