Hiya! AskHistorians can't do your homework for you, but we can give you some guidance and further resources. You might start by thinking about these two points:

1. The Middle Ages are often said to last until 1453, even 1500. Yet the "Renaissance" is gearing up by the later 1300s. Does that suggest a sharp break between the social classes of the M.A. and the Renaissance era? Would everything change everywhere overnight?

2. Think about the environment in which people lived. In the Middle Ages, you're probably picturing peasants on their farms, aristocrats in their castles, and monks and nuns in their monasteries, right? Now think about the Renaissance. What living environment comes to your mind? What classes of people might live in that environment? What types of activity are necessary under those conditions versus the ones discussed in the Middle Ages?

The Renaissance is not a historical era per se, but rather a movement that fits within the medieval to early modern transition, and it's largely cultural in nature, particularly artistic, so it doesn't make much sense to ask about social structure in the Renaissance in comparison to that in the Middle Ages, but the term is widely misused, so it's still pretty clear what you're asking about.

First of all, the three estates are not a clear-cut division that was implemented conscienciously in Europe during the Middle Ages, it is rather a theoretical model for society devised in the 11th century starting with the writings of Bishop Adalberon of Laon. If it is broken down to its most basic core, it applies to many different social scenarios, but such a broad categorisation of society is hardly descriptive of the reality of the time. The problem here is that the third estate includes a very broad range of people who perfomred many different jobs and who fit highly varying degrees of economic and legal status (basically lumping up unlanded day labourers and wealthy merchants and urban-elite types into the same category). In very rough brushes, the model of the tripartite society grows increasingly less accurate as we move from the High Middle Ages into the Late Middle Ages and the Early Modern Era, as commerce grows and economies become more specialised. This is a very broad overview and, I should emphsasise that the model is of very limited practical application since the moment of its inception. I should also mention that I'm entirely ignorant of the standards used in grading the exam you are about to take, so if you've seen the tripartite division used extensively in your manuals, you should consider just going along with it.