I have a wireless router linksys connected to the modern witch is on the second floor. I want to connect another router linksys on the same network that the one on the second floor is on, wirelessly without any cords on the first floor. How can I do that help please.
How's about a powerline adapter? About 35 quid, and nice and easy to fit. You can then plug each router into one of the adapters, and use one as a router, and one as a repeater (providing your router supports this).
I assume you want to do this so that you can attach a couple devices that don't have wireless capability. If you only want to connect one device, you can use something like a media bridge or a gaming bridge/adapter that provides 1 ethernet port.
If you need to attach several pieces of gear via ethernet, then look up bridge mode or client bridge mode.
I recommend that both devices be the same brand. If possible, I also recommend using DD-WRT firmware as that's what I've used to do exactly what you describe and there's tons of info on how to do it online.
I would go with the Cisco/Linksys wireless extender/repeater - instructions are simple as long as you're configuring from a laptop connected to the wireless network you want to extender. That's what I am using to get full signal throughout my house.
Yup! I was fixing to say something about DD-WRT but be certain that it is a router that you don't need elsewhere because you may not be able to flash it back.
Some of the higher-end routers (N600 and up) should also support Gateway or Ad-Hoc mode both wired and wirelessly. Not sure why you would want 2 wireless routers on the same network though cause you will get the same coverage out of a Powerline AV adapter or a repeater and don't have to worry about computers getting confused on the network as to who is talking to what.