First, keep in mind that Florence is pretty small. The Hotel Brunelleschi is very central in the heart of the historical center. From here you can either walk up to the Piazzale or take the bus - although you'll need to walk a little to make it to the bus stop (for bus #13) that would take you up there.
You should read this post I had already answered about how to get up there - I had made a map to show the various walking routes you can take as well as show where the bus stops are - hope it is useful! How to get to Piazzale Michelangelo - walking or with bus. If you have any questions about the routes, feel free to ask!
p.s. you can also head to the SMN train station and get on bus #12 or 13 to get to Piazzale Michelangelo - it will take a while because it first goes around the city but you'll get to see more of the Florence that you would otherwise, even if it is from the bus windows!