Question slow download , fast upload over WiFi

[omaryessam]

through the cable , every things works just fine (25Mbps/6Mbps) . but over wifi the download speed is 2 and the upload is normal (6Mbps) .
i use TP-Link W9960 modem router . some said that disabling WMM solve it but i cat even disable it

 

[rgd1101]

and what the device having slow download?