It's pretty easy:
- Get an external drive. Make sure it's formatted. I prefer to have a drive specifically for samples - including Ableton Live packs, Kontakt libraries, and Reason refills.
- Move the Factory Packs from their default location to the new drive. <cmd>-drag on OSX. I put them on my external USB drive called "Sample Libraries" in a folder called "Ableton/Factory Packs".
- Start up Live 9 - click on 'Packs' in the browser in the 'PLACES' section. The libraries you moved will appear gray.
- Right click each gray library, select 'Locate library', and browser for the folder in the new location.