I've never used "re-study".
The word "revise", when used in connection with exams (in the UK) has a very specific meaning. It is what you do at home (or on the bus or outside school hours), in your own time, trying to go over and over all the stuff you've learnt in the last 1/2 years in class, basically trying to memorise it all. When I was at secondary school, for about a month before our final exams, we all got at least one "revision period" (just one hour) each week, which could be used for any subject we chose. Of course, we were also expected to revise at home too. In all honesty, most of my revision got done the night before an exam and, in desperation, over breakfast on the morning of the exam.