SETTING UP TWO DIFFERENT ISPs ON A LAN NETWORK.

Hi, I have two offices on a building. One is on the fourteenth floor while the other is on ground floor. My Router, servers and and two switches are downstairs while I have two switches on the fourteenth floor. All switches are linked together with a fibre optic cable from the ground floor to the fourteenth floor. With one router serving as my DHCP and DNS. How can I configure another router on the network so that those on the fourteenth floor uses another ISP while ground floor use anoth ISP. Yet making sure that all have assess to the server on ground floor?