D-link 2750u Quality of Service (QoS) Configurations

Hi all. I have a d-link 2750u modem/router, and I need to know how to configure its goddamn QoS from 0 to 100! (It's driving me mad.) Can you PLEASE help me do this?

Details: The modem is the first place where we get internet, then, its wireless singals are amplified using a Universal Wireless Repeater (a tenda W3002R router), then, I have connected an android box (the device to have the most bandwidth usage, for streaming full hd content smoothly under any circumstances) to the Tenda router VIA CABLE, and at the meantime, I want to connect plenty of other wireless (mostly) and wired devices to either the D-link or the Tenda router, of course with lower bandwidth usage priorities.

Thanks a MILLION in advance... And any technician's guidance will benefit lots of peaple on this issue, not just me, for this is pretty advanced configuration. Thnx again.