I am not an expert on Brazil, so I am going to dodge that part of your question. Since you’re studying for an exam, telling you my answers probably wouldn't help you much since I don’t know exactly what your teacher/professor has covered. To give you some direction though, I recommend you look up the growing discontent among the creole elite at their exclusion from positions of power in the Spanish Empire. Consider how the Bourbon Reforms were leading to a centralization of state power, taking away autonomy from colonial authorities. Next, examine the trade restrictions in place within the Spanish Empire in an era of growing free trade. Spain’s empire was dominated by mercantile economic systems which were state of the art in the early 1500s but were struggling to keep pace by the late 1700s. I would also recommend that you delve into the growing influence of Enlightenment thought on both sides of the Atlantic. Although Spain has a reputation for being dogmatic, this is really not accurate. The elite had access to Enlightenment philosophy, which was clearly reflected in independence era discourses about political participation, republican values, and the formation of una nación. The elite on both sides of the Atlantic were reimagining the forms state power. Finally, you might consider how commoner revolts like Túpac Amaru demonstrated discontent among the lower class populations who were excluded from most Spanish systems of power. Are these revolts expressions of popular discontent at the status quo? How much had Spain worked to incorporate diverse peoples into a unified populous? (Hint: Very little)

I’ll be honest, I really don’t like the second part of the question. Spanish leaders couldn't see the future, so they obviously didn't know that their empire was about to collapse (independence was a spontaneous event), so they were not making changes to save the empire or prevent independence. Instead, their changes to the colonies must be understood in the context of late eighteenth century political, economic, and social changes that necessitated adjustment to the colonial administration. My criticism of the question aside, you could discuss how Spanish authorities “doubled down” on centralization. The Spanish Empire was restructured to include two new viceroyalties to improve colonial administration and oversight. The monarchy expelled the Jesuits who were seen as too independent of the Crown. Spain implemented modest changes in trade restrictions to improve finances in the Empire, and there was even talk among Spanish authorities of lifting the colonies onto equal footing with Spain (which was interrupted by Napoleon’s invasion). They worked to improve imperial defense against foreign interlopers and sent a variety of military and scientific expeditions to examine imperial holdings. Additionally, consider responses to colonial revolts. These were often very harsh both before and during the independence period. Finally, look up what Spain did to retain Cuba, their most important colony, following the loss of most of their continental territory. Spain made a number of changes that appeased the colonial elite for most of the nineteenth century.

Finally, check out some of the discussions we have had on AskHistorians in the past about the decline of Spain and the breakdown of Spanish America after the revolutions. I think a number of these discussions are quite good and provide a variety of perspectives on independence that might aid in your studies. Good luck on your exam!