Well, I am confused ! Why do you want to do that?
- Do you want to quit engineering and take up psychology as a full-time career? OR
- Do you want to remain an engineer but have some interest in psychology and wish to pursue that interest?
If you want to just learn about basics of psychology, maybe you can look up some online courses. IGNOU, New Delhi has some courses which you can do part-time. That way you can remain in your engineering profession and maintain your interest in psychology.
BUT. But, if you want to quit engineering and get into psychology, you will have to search for a graduate level course in psychology. That will put you back by 4 years if you have already completed engineering degree. However, if you are passionate about psychology and see a career in that field, it could be worthwhile.
Follow your heart, and all will be well.