Look for a router with the best range/speed combo

Hi there,

I hope I'm in the right place! I'm looking for a router with the best range (vertical, if that matters). I live in a three story building, the bottom level being the garage where the router is located. I'm not the most tech savvy person, but my provider hooked up the router there, and I dont think I can move it. Regardless, my signal on the third floor is absolutely awful and I need to improve it.

Im assuming my best option is to buy a new router, but I have no clue what to get. The current router is a Motorola SURFboard SBG6782.

Any help is appreciated! If you need more info just let me know.