How to upgrade from PostgreSQL v9.1.2 to v9.5.3?

Hello:

I'm new to the mailing list, and an admitted novice at using PostgreSQL.
I inherited a Surround SCM data server (Seapine Software) that runs on
PostgreSQL server v9.1.2 running on a Mac Pro 6.1 (Late 2013) in OS X
10.10.5 (Yosemite). Eventually I will have to migrate the entire server
data base (both Surround SCM and PostgreSQL) to a PC running Windows or
Linux, because Seapine has dropped support for OS X. But that comes later.

For now, I just want to upgrade the PostgreSQL server from v9.1.2 to
v9.5.3 so everything will be running the latest software BEFORE I
migrate to the new PC server host. I assume that means that I have to
back up the entire PostgreSQL cluster in v9.1.2, then install v9.5.3,
and then restore from the backup.

I have studied the PostgreSQL documentation, Section 17.6. Upgrading a
PostgreSQL Cluster for v9.5.3
<https://www.postgresql.org/docs/current/static/upgrading.html>. It's
somewhat confusing (especially paragraph 1 in Section 17.6.1. Upgrading
Data via pg_dumpall
<https://www.postgresql.org/docs/9.4/static/upgrading.html#UPGRADING-VIA-PGDUMPALL>,
which seems to say that I should use v9.5.3 to make the backup that I
need to make BEFORE I upgrade to v9.5.3. Sounds like a Catch-22...but
whatever the case, it seems clear that I need to run *pg_dumpall* to
make the backup.

There's my problem. I'm using *pgAdmin3, v1.14.1* for backup and
restore, and apparently the *Backup...* menu command only does a
*pg_dump*, not a *pg_dumpall*. I know that I can run *pg_dumpall* as a
command line process from Terminal.app, but I'm close to completely
ignorant about how to do that.

I follow instructions pretty well if they're clearly spelled out step by
step, but everything I've read so far assumes that I know more about how
to use command line than I actually know. If someone can point me toward
a step by step set of instructions for a total noob, I could probably
take it from there.

I know how to specify file paths, and I've already created a
*/usr/local/pg-dumpall* directory where the backup file can be written,
but I need to know how to get the *pg_dumpall* process to actually run.
It's probably best to assume I know nothing except how to start
Terminal.app.

Oh...and it's my understanding that later versions of PostgreSQL (e.g.,
v9.4.8) include a *pg_upgrade* process that makes the upgrade process
easier. However, there's no such feature in v9.1.2.

Thanks!

Nigel