How to upgrade bash to v4.0+ properly?

I'm on OS X 10.10.2 and

$ /bin/bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin14)
Copyright (C) 2007 Free Software Foundation, Inc.

How to upgrade bash to v4.0+ properly?

Update:

After installing bash with pkgsrc

 pkgin install bash

I got newer bash but it isn't default:

$ which bash
/bin/bash
$ /usr/pkg/bin/bash --version
GNU bash, version 4.3.30(1)-release (x86_64-apple-darwin13)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://ift.tt/KpOJT7;

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin14)
Copyright (C) 2007 Free Software Foundation, Inc.

How to make the newer bash the default one?