As of now (April 2018) you can change the wake word "Alexa" to "Echo," "Amazon" or "Computer."
To do this go into your Alexa app settings, click on an Echo device, and scroll down to the wake word setting. From there you can make your selection and save your new wake word.
You can only change one device's wake word at a time in the settings menu. There is no current information regarding if more names or customized names will be added.