Yes, you can cancel long-term plans by sending us a Support request. You will only be charged for the days that you used (deducting discounts for long-term plans).
For example, if you purchase a 6-month plan and receive a 25% discount for it, and you choose to cancel after one month, then you will be charged only the full monthly price (what you would have paid if you didn't buy a 6-month plan). The remainder will be returned to you.
Remember, you can always pause your subscription for 7, 14 or 21 days (max of one pause per subscription month). You can do it from your subscription page inside your student account.
Alternatively you can also downgrade your plan to a smaller one and receive a refund for the difference in cost. Again, you can make changes from your subscription page.