Consult your academic advisor or guidance counselor, if your university assigns you one. Discuss the planned switch with your advisor to solicit their advice and be informed of the process involved in switching.
Declare your new major with the office of the registrar or whichever department within your university handles course and major changes.
Consult the course requirements for an engineering degree at your school to determine which courses you need to complete.
Formulate a year-by-year schedule to determine how you will complete the required coursework. This will vary greatly by institution and engineering specialization, but generally, engineering degrees require a strong background in advanced math, physics, chemistry and other courses in the hard sciences.
Complete the engineering coursework according to your yearly plan.