Answer:
There were several changes in painting that were important.
One was the introduction of oil paint as the only paints used for a painting. During the Middle Ages, paintings were done using tempera, with early oil paints used only where details demanded them. In the Renaissance, oils were improved to the point that an artist could use them exclusively.
Another change was the introduction of linear perspective, which is more like photographic perspective. During the Middle Ages, the perspective systems used were based on the importance of subject, with the most important being largest, or such things as reverse perspective, where the more distant things were larger. Renaissance artists tended to use linear perspective exclusively.
Subject matter of paintings changed. During the Middle Ages, people were much more interested in religious subjects, representations of important people, such as kings, or representations of anonymous ordinary people as a decorative element for texts, such as pictures of peasants working in the fields illustrating texts. During the Renaissance, the subjects of the paintings became more secular, and more focused on wealthy middle class people or subjects derived from classical mythology.