How to tell my research advisor I'd like to drop a class?
Dear Supervisor,
  
  I am taking the AI course.  I need X hours/week to do well in this
  course.  My other courses only take Y hours/week.  I am considering
  dropping this elective course so that I can devote X more hours/week
  to my research.  Do you think this is a good idea?
  
  Thanks for your advice, 
  
  Student


Note:  Most likely your advisor will support you if you want to spend time on research.  But they may know something you did not tell us on Stack Exchange.  If your advisor says no, you can still tell them you have decided to drop the course.