Yes, you really can change your Pokemon Go username but be warned, you can only change it ONCE so choose very carefully!
It’s dead simple. First you hit the menu button (the red/white ball at the bottom of the screen.)
Then you click on the settings gear (the flower/wheel at the top right of the screen.)
From there you just click to change your name
Think carefully, remember, you can only change it ONCE. Try not to include your real name.
Play safe and have fun!