What can a student who is already studying hard do to improve low grades? I have been studying hard for the past year and a half (it's my second year of Computer Science) while not getting remotely close to the desired results. I passed my first year with a 7.2 GPA (5 (failing grade) - 6 - 7 - 8 - 9 - 10 (best)) which is very low given that I want to master in applied maths or an area revolving around that.

I'm doing 6 hours a day Monday to Thursday, 10 hours a day Friday and Saturday, and on Sunday I try to rest a little. I rest every 30-45 minutes for 5-15 minutes. Now, I'm isolating myself, sacrificing my social life, among other things. I'm feeling angry at myself every time I get the exam results or when a deadline passes and I haven't finished the lab/project.

I even started eating healthier because I thought unhealthy food was the problem.

What can a student in this situation do to earn better grades?

P.S: I do like what I study, no matter how angry I get, I know I will wake up the next day and head to the library/school.
Don't panic. The fact that you're still enthusiastic about your studies suggests to me that you can likely fix the problem, whatever it is.

If you're having trouble with just one or two of your subjects, then there's probably a gap in your background knowledge. Try to figure out where that gap is. Right now it may feel like everything in those subjects is difficult, but I suspect if you look hard, you'll find out there's just one or two small gaps in your knowledge, and that's something you can remedy. Perhaps you can take a lighter course load next semester to give you time to focus on the areas you're having difficulty. Once you figure out what the gaps are, you could either take the appropriate course, or teach yourself. This strategy may delay your graduation by a semester, but it could be worth it.

If you're having trouble with most of your subjects, then I suspect you're not studying very efficiently. You may be working hard, but not using your time well. Unfortunately, I don't have specific advice on how to improve your study habits, but there are lots of resources available for this kind of thing, and others here may be able to point you to those resources. Again, it might be worthwhile to take a lighter course load while you practice your new study habits.

Talk to your student advisor about your problem. If you think it's a gap in your foundational knowledge, t may be worthwhile to pick one problem that you found particularly difficult, and ask the instructor (during office hours, not in class) to go through it in gory detail with you to help you figure out where your knowledge gaps are. 

Also, there is probably a student centre or something like that at your school, where you can get advice on how to improve your study habits.