Postgres UPGRADE from 9.2 to 9.4

Hi guys,

I'll be migrating my Postgres 9.2 database from Rackspace to Amazon.

To do that work, I'll be using DMS at amazon... unfortunately DMS needs a
Postgres 9.4+ version at least (
http://docs.aws.amazon.com/pt_br/dms/latest/userguide/CHAP_Introduction.Sources.html)
- So that means that I'll have to upgrade my postgres version.

Questions:

1 - I'll have to upgrade the version on my Master server, right? I can't
upgrade only in a streaming replication slave server, right?

2 - I've never done a Postgres upgrade before, can you give some guide
here? Is usually a easy thing? How long can it take? Is a downtime needed?

Thanks guys,
Patrick