Melpa : The largest and most up-to-date repository of Emacs packages.

Enable it

To enable Emacs Melpa packages you have to add this to your emacs config.

;; melpa packages
(require 'package)
(add-to-list 'package-archives
              '("melpa" . "http://melpa.org/packages/") t)

How to Install Packages Using ELPA

Call ‘M-x list-packages’.
Find the package you want, move cursor to the line press Enter ↵.
press Tab ↹ to move cursor to the “Install” button then press Enter ↵.
Then, you can start to use the package.

How to Upgrade packaegs

The command M-x list-packages brings up the package menu.

In there use U to mark all upgradable packages to be upgraded, and x to actually perform the new updates.

• U

  Mark all package with a newer available version for upgrading (package-menu-mark-upgrades). 
  This places an installation mark on the new available versions, and a deletion mark on the 
  old installed versions (marked with status ‘obsolete’).

• x

  Download and install all packages marked with i, and their dependencies; also, delete all 
  packages marked with d (package-menu-execute). This also removes the marks.