Quero muda minha senha como fasso?

Can any one tell me the difference between Archer C1200(3 antennas) and C6 Ac1200(4 antennas) l, Except the usb port difference, and which one is better.

i have 2 tp link routers 1. 150Mbps Wireless N Router TL-WR740N ver - 6.0 (main router - have internet acces via optical fiber ont) 2. 300Mbps Wireless N USB ADSL2+ Modem Router TD-W8968 ver-4.0 (seco