If you were admitted to Engineering but already know you want to pursue a different major, tell your academic advisor during the course selection process. Your advisor will help you select the appropriate classes for that major.
You are expected to take charge of your change of major by doing the following:
Visit the department website of your prospective major
Follow their instructions for the change of major process (each department has its own requirements and procedures.) If you are unsure of the process call or visit the department to ask!
When you have met the requirements, meet with an advisor in that department to officially change your major.