Scroll down in the developer options menu until you find the windows, transition, and animator scale settings.
A quick sidenote: It might be tempting to check out all the other options and settings in the Android developer options. I would suggest staying away from playing around with all these extra settings, as I can't guarantee that the phone will work properly if you do.
Changing the animation scale settings in the developer options, however, doesn't mess with your phone at all. I've done this to dozens of Android smartphones and have never encountered an issue.