As you may have seen, PostgreSQL 9.1 has now reached its End of Life.
That means the last maintenance update of 9.1 will be in November 2016.
PostgreSQL 9.6 is currently due out in September 2016, so you have a chance to move from PostgreSQL 9.1 to PostgreSQL 9.6.
Supported upgrade choices are
- pg_dump and pg_restore
both of which require downtime, which will increase according to the size of the database.
Other options to reduce downtime are
- Use Slony or Londiste, if the performance is good enough to allow it
- Use the new 2ndQuadrant logical upgrade service to take you from 9.1 to 9.4, 9.5 or 9.6
PostgreSQL upgrades for 9.2 and 9.3 will be available in 2017.