I live in an old house with no cable jacks. When we got xfinity internet/phone, they drilled a hole in my living room wall and placed a coax jack. At this point, I'm wanting to move the router upstairs. We would need to drill another hole in the upstairs wall and run a line from the plastic box outside, correct? Would there be any splitters involved since I no longer intend to use the downstairs jack? Thanks.
Assuming the splitter is in the box outside, yes you want a new line from upstairs to that splitter. Use RG6 coax of the shortest length possible and use the proper fittings.