How to Install GIMP 2.8.20 in Ubuntu

The new release has been made into the PPA repository, available for all current Ubuntu releases and derivatives.

1. To add the PPA, open terminal (Ctrl+Alt+T) and run command:

sudo add-apt-repository ppa:otto-kesselgulasch/gimp

2. You can then upgrade the editor from a previous release via Software Updater utility:

Or install GIMP either via Synaptic Package Manager or command:

sudo apt-get update

sudo apt-get install gimp

Uninstall:

To restore GIMP to the stock versions available in Ubuntu main repositories, open terminal and purge the PPA via ppa-purge tool:

sudo apt-get ppa-purge && sudo ppa-purge ppa:otto-kesselgulasch/gimp

출처 : http://ubuntuhandbook.org/index.php/page/3/