It may be best to treat studying for a degree as though it were a full time job, and aim to work for thirty five to forty hours a week, making sure to take time off to eat, sleep, exercise, and socialise.
There is no substitute for reading the judgments and legislative provisions most relevant to each of the subjects which you study. A textbook or casebook is the basic guide, but it's best to read cases rather than commentaries on cases. How much more you should read depends on the way in which your course is structured and taught, and on which essays you are asked to write and what other types of work you are asked to undertake.
I suggest that you talk to one or more of your tutors about ideas for managing the workload.
You may find that, as you become more experienced, you adjust to the workload. University is a big step up from sixth form, and law is a demanding subject. The study of law is by is nature labour-intensive. If you are thinking of becoming a lawyer, please note that the practice of law is in most cases more labour-intensive than the study of law.
If you find that you can't adjust to the workload by, say, the end of your first year, you may at that point wish to consider whether to ask your university or another university to accept you as a student in another subject. There is no point in plugging on with a course of study if you don't enjoy it and can't do well in it.
As for essays, the key thing is to make sure that you identify and write about every point raised by the question. Consult the course handbook for your degree to see what your university is looking for in an essay. Universities differ in their approach to teaching and to assessing students' written work, so generic answers to your question about essays may be of little practical utility.