Slow Browsing Speeds On Router

I have V-Fiber with the Beetel modem (777VR1). I have connected a D-Link router to it, so that I get more range, but my download speed on the router is much lower than that of the modem. I get 40 down and 6-8 up on the modem while on the router it is very low. BTW, I do not physically connect to the devices, I'm connecting via Wi-Fi.