Inspiron 17 3000

The download internet speed is between 10-40 MB/s. I do have 350 provided by my ISP. They can increase it to 500 MB/s, but our older laptops are able to handle maximum 350 MB/s. We bought two identicall Inspiron 17 3000 just for the reason to use fully internet speed. At the beginning we had around 2 MB/s download. Googled for all possible solutions finally removed properly SmartByte. The speed increased to just 10-40 MB/s. Also got involved two other IT guys checking everything else and still no solution. We all spent on it maybe 15 hours in total and still no solution. All other devices here (old HP laptops, Linksys mesh, etc.) are showing 350 MB/s. 
Upload is fine. Only download is super slow. What else can I do. It's extremely frustrating.
Please help.