Three routers and one wi-fi network

Hello,
I have three mikrotik 2011UiAS-2HnD routers. One on each floor of my house. Only main router in basement (192.168.11.1) has DHCP. AP1(192.168.11.2) and AP2(192.168.11.3) are connected to main router by ethernet cable. Network wortks, i have acces to WEB and all devices see each other but i have problem with switching beetwen AP. If I was previously connected to AP2 and I approach AP3, I am still connected to AP2 despite a very weak signal.

And here comes my question: How to connect these routers so that the device switches itself to AP with the strongest signal ?

Thank you in advance for your help and support!