There are many resources to help you choose a specialization, either in Architecture, Planning, Landscape or Design Studies. The lower-division ENVD core classes will give a good introduction to the different majors - so just by taking those you'll be exploring the options. You can also learn more about each major by visiting with advisors and talking to your professors.
You can declare your specialization the first day of class but no later than the second semester of your third year. You can change your specialization at any time with your academic advisor. If you are near graduation, a change of specialization may affect your graduation timeline, so we would recommend meeting with an advisor to discuss your options.