Depending upon if the router is set to auto DNS, then you can click on TCP/IPv4/Properties as illustrated in the following MS tutorial then follow the steps in Step 6 Change TCP/IP settings
If the router is set to use a specific DNS server, then changing it in the computer can cause a conflict and prevent connectivity so just try it on the wireless adapter.
To access the window illustrated in the tutorial rather than use that method - right click on the wifi icon in the system tray and click on Open Network and Sharing Center - click on Change adapter settings (left pane) and then right click on the wireless adapter then on Properties.
After you have entered the new DNS settings, tick the box for Validate settings upon exit - Ok - Close and Windows troubleshooter will kick in and if all is well, then it will say that it can't ID any problem.
You could try changing to either Google - Primary 126.96.36.199 / Secondary 188.8.131.52 or Open DNS - Primary 184.108.40.206 / Secondary 220.127.116.11 and see if it makes any difference.
I can't quite see that it would have anything to do with your ISP as it would affect all video downloads, unless you are just experiencing the slow downloads at peak times - either due to popularity or throttling by your ISP, but you could ask them about that.