Switch between spyder for python 2 and 3

Spyder is launched from the environment that you're using.

So if you want to use python 3 in Spyder then you activate python34 (or whatever you named the environment with Python 3) then run spyder.

If you want to use python 2 in Spyder then you deactivate the python3 environment (or activate an environment in which you installed Python 2) then run spyder.

I do not believe that you can change environments once Spyder is launched.

N.B. you may need to install Spyder in each environment, depending on your set up, by first activating the environment then using conda install spyder.