Question about setting up old router as an AP

I upgraded my fios router from an G1100 to G3100 that is set up on the second floor of the house. The first floor doesn’t get a good signal so we want to use the G1100 as an AP and place it on the first floor. In the settings of the AP I was told to disable the DHCP. Is it possible to change the SSID of the AP to same name as the new router? Hypothetically speaking will a device know which signal to choose on the first floor? Will it automatically choose the stronger signal? What is the best practice for setting up a router as an AP? Thanks!