How to undo or clean build_packages & build_image

Dear Chromium OS team,

I am try to undo or clean build_packages & build_image, which I executed as below, may I know please, if there is any possible way to undo or clean build_packages & build_image, as it is consuming lots of hard disk space

ie., How to undo or clean : 

build_packages –board=<board> –autosetgov, 

build_image –board=<board> –enable_serial “ttyS0,115200,8n1 no_console_suspend” –noenable_rootfs_verification test

Kindly do the needful

Many thanks in advance,