delete old pc connections

like the title says, over the years i have connected computers to my network, and after os updates have stayed in my network like a sore thumb. How do i get rid of them? screenshot below for better understanding. the ones in yellow are not active pcs anymore, i want to get rid of those. thanks.

i fixed it :)

Open the command prompt in administrator mode and type

Code:

ipconfig /flushdns

and reboot. if this doesn't work, check your router and see if it isn't keeping old inactive pc in your network.