I have been a trial member for Amazon Prime student and it has been great with free two-day shipping and such. However, there's a recent bump on membership pricing which brings my attention to find out if I should sign up for the monthly membership or the annual membership.
It turns out the monthly membership fee has been increased from 5.49 a month to 6.49 a month, rendering a 12 dollar increase a year compared to the same annual membership fee 49 a year. Therefore I was browsing my amazon account, and I found out the place you need to make the switch is in the Your Account/Manage Your Prime Membership (see the picture). Simply select the Annual option and
you have saved 12 dollars. :)