Whats your mobo model? Most models come with 1gbps lan/Ethernet port.
Seems yours is manually set to 10/100mbps or if auto-negotiation then first try to manually change the speed of Ethernet to 1gbps. Else the Ethernet cable needs to be replaced with an cat5e.
which option should I select in all of them I dont know. the internet guy has done new installation of fiber optic cable. remove the cable of 50 mbps speed and installed new fiber optic cable completely. He also said it has glass thing inside the wire and not to bend at all otherwise glass breaks in that. After reading your comment I did R&D and found out to select speed and duplex option in advanced which I just selected and change it 1 GB full duplex but even after doing that it shows 100 mbps speed only. But there is 1 more suggestion this point. Make sure that the Microsoft Network Client option is checked. but no ways are shown how to do that.
If your PC do not have Gigabit LAN port, You can buy something like this.
Before buying also check your PC has empty compatible PCIE slot.
Can u find it out if the one you just suggested is compatible or not
I researched and found this it wont support it says the existing that I have
What Is the Speed of Realtek PCIe GBE Family Controller?
If your Realtek network interface controller is a 2.5G Gigabit Ethernet, then the maximum speed is 2.5GB/sec.
If your Realtek network interface controller is 10/100/1000M Gigabit Ethernet, then it can deliver up to 1000 MB/sec internet speed.
If your Realtek PCIe FE Family Controller is a 10/100M network device, it means its maximum speed is 100 MB/sec. FE means Fast Ethernet that is 10/100 MB/sec.