$ conda info --envs
# conda environments:
#
CarND-TensorFlow-Lab /Users/ukilucas/anaconda3/envs/CarND-TensorFlow-Lab
IntroToTensorFlow /Users/ukilucas/anaconda3/envs/IntroToTensorFlow
py3 /Users/ukilucas/anaconda3/envs/py3
py35 /Users/ukilucas/anaconda3/envs/py35
root * /Users/ukilucas/anaconda3
to do so I use command
$ conda env remove --name IntroToTensorFlow
$ conda info --envs
# conda environments:
#
py35 * /Users/ukilucas/anaconda3/envs/py35
root /Users/ukilucas/anaconda3
(py35) $ python --version
Python 3.5.2 :: Anaconda 4.2.0 (x86_64)