I think you have a router with a custom firmware, because that is not the interface found in a dlink router. That being said, I will do my best to help you.
The first thing you must learn about QoS is that, home router QoS like this one is not really QoS. It is just traffic shaping. And you can only do so much with a device like this. The second thing is that you either get max bandwidth or low latency. You can’t have both. If you want really low latency, you must sacrifice some bandwidth. There is no way around this with a home router.
Your first task is to redo your speedtest at different times of the day and write them down. There is probably some oscillation in your speed and you must discover your lowest one. You must write down the lowest value you get for download and the lowest value you get for upload, even if they didn’t happen at the same time.
Lets assume that your lowest speed is 46,3 Mbit/s and 8,7 Mbit/s. I will do all calculations assuming these values. Please use the real values that you get.
You will now take 15% off of those speeds and input these values at the router speeds. (That is correct, you will forfeit 15% of your bandwidth in order to be able to control your traffic)
Download: 46,3 * 1024 * 0,85 = 40300
Upload: 8,7 * 1024 * 0,85 = 7573
You will input 40300 and 7573.
After that you must create a rule for each IP in your network. Lets assume you have 3 computers:
192.168.0.100 - That’s your computer that needs prioritizing
192.168.0.101 - That is a friend computer
192.168.0.110 - That is some other friend computer
Your first rule is to guarantee bandwidth for you.
Put your IP as start and finish like this: 192.168.0.100 - 192.168.0.100 (you can put your MAC address instead, if you know how to get it).
Put your uplink as 10% (you can change this percentage to whatever you want) of your maximum: 757 and 4030.
The other rules are to apply QoS to the other computers, without them QoS will not work.
Put other IP’s as a range: 192.168.0.101 - 192.168.0.110
Put this rule guarantee bandwidth as 20% (you can change this too as you please): 1514 and 8060.
After you apply these rules and save, your QoS must be working. But just to be sure, power cycle your router after you save. That is, take it off the power plug, wait 15 seconds and put on the power again.
This is how you should test it:
1 - Download the software ping plotter freeware at this address:
https://www.pingplotter.com/freeware.html
2 - Make sure your computer is the only one connected to the network. You need to do this for testing.
3 - Start pinging www.google.com. Set the trace interval to 1 second. Set focus time to 10 traces or 10 seconds.
4 - This software will show ping responses from all servers between you and google. You should be looking at the first non-local value.
5 - Your local responses (probably your router) will respond with something between 0ms and 2ms. You should look at the first line that have a bigger value like 10ms or 15ms or 20ms (For a slow connection like mine they are around 50ms). This line contains the first server that your traffic reaches at your ISP.
6 - Take note of what is the typical response time for this server.
7 - Now you should connect other computers to the network and make them download or upload a big file. Usually I start downloading a linux distribution like ubuntu via torrent.
8 - Wait until the download start using a lot of bandwidth. This should take some time in a torrent, but probably will be fast for a web download.
9 - Go back to your computer and see how much your ping is varying. If QoS is working, even if your ping varies, the average should be close to your original value. If your average ping is bigger than 100ms your QoS is not working.
If after this config your QoS is not working then your firmware is probably broken and I can’t help you.
If you do get your QoS to work, please get back to me, because I’m considering buying the same router you have.
Sorry for my bad english and feel free to ask me about your doubts.