Slow Internet speeds

My connection is not horrible as I have the ultimate package(150Mbps) but I do not get the speeds as promised. I have been running the speed test consistently over the last couple months and I have never gotten over 50Mbps DL and its usually below 25Mbps. Upload is usually the same or worse. I just ran the check and this is what I received: Start: Mon Aug 3 6:10 PM Cox Net: Yes DL speed:12 Mbps UL speed:23 Mbps Latency:12 millisec Cox Market: Phoenix I have the C6300BD Netgear that I received from Cox the when I signed up for the package in March. I have never really complained about the service but as I have been getting more electronic devices I have been noticing the lag. Also, I just ordered a 4K TV, so I will be needing the faster speeds. I make sure when I do the checks that the only device connected is my computer that is hard wired to the router. Can you please let me know what I need to do or what the solution could be? I have ran the test with my phones and get the same outcome via Wi-Fi.