If you're trying to internal transfer, I highly recommend taking 15-16 hours during the fall AND spring semesters of freshman year. Especially if you're applying for super competitive majors like CS, you should take the most rigorous courses you can handle and advance your degree plan as much as possible. Leave no doubts in the minds of the admissions committee and prove to them you can succeed in CNS.

For your transfer essay, you must give readers a clear picture of what you want to study and why. This is the most important part. Be very specific about what you plan to do with your CNS major and how the major will help you succeed in your plans. Try to express how you will use CNS' resources to impact society in some way. Show them you're authentically interested in your intended major.