How can I improve my download speed

My usuall download speed stays around 3 MBps but somedays and, specially in the morning, it reaches 5 (one time 10!), other days, specially at night, it stays in 1.

This makes sense since the way the internet reaches my pc from the downstairs router is from an extension (just one piece) conencted conected to other diferent extension (one piece conected to the source and other to the pc). So, i guess, at night, when the lights are on, theres much more "turbulence" in the power grid.

Now, I have tried plenty of things to try and improve. I first tryed to put the two part extension directly connect from the router to the pc but it slowed down considerably. I tried to do the same thung with the one piece extension and it slightly decreases compared to the original setup. I have tried multiple locations to put the extensions but none were better than what they already were.

I cant place the router on my bedroom as the fiber doesnt pass throught there.

Is there anything I can do?