There are at least two ways in which the Northern Renaissance led to the Reformation.
First of all, the Renaissance spread ideas of humanism. These ideas, put forward by such people as Erasmus, held that people were capable of a great deal of understanding and intelligence. They were, for example, capable of understanding a great deal about God and religion. This sort of idea led to a questioning of the Catholic Church since the Church taught that people had to simply do as they were told by those (the clergy) who were actually capable of understanding God. Humanism, then, set the stage for the Protestant idea that people could interact with and understand God by themselves.
Second, the technological advances of the Renaissance helped lead to the invention of the printing press. This invention allowed works of humanism and, very importantly, Bibles in the vernacular, to become relatively widely available. When this happened, people were able to read and think more about religion and God. This, too, turned them towards Protestant ideas.
In these ways, both the ideas and the technology of the Renaissance helped lead to the Reformation.
By the time of the Northern Renaissance, the system of feudalism was weakening in Northern Europe. The Roman Catholic church had been a vital part of feudalism, as it supported lords in return for their financial support. As feudalism weakened, so did the Catholic Church.
In addition, the Renaissance involved ideas of humanism, centered on the concerns of humans, and away from religion. These ideas, which surfaced in art, also weakened the hold of the Roman Catholic church on society and led people to question authority, part of what caused the Protestant Reformation. In addition, new forms of technology such as the printing press led to the dissemination of ideas, planting the seeds of revolt and questioning in people's minds. New forms of technology and the belief in humanism also resulted in the growth of scientific inquiry, which also weakened people's faith in traditional religion. As people discovered the way the natural world worked, they began to question traditional forms of religion and were interested in new forms of religion.