Aladdad :
Yes, I have a Fiber Modem that connects to the internet/Phone. From that i have 2 cables coming out from it. one going to my main PC "motherboard" and another cable going to a router on the 2nd floor. on the Devices connected to the router upstairs are able to get full 200mbit/s internet speed. While my PC in the first floor can only get 100Mbit/s i hope this clarify
If you have more than one ethernet cable coming from the "modem" then it sounds like it already has a ROUTER built into it.
If so, I would not use a second router. I would use a Gb switch instead. Like THIS:
http://www.newegg.com/Product/Product.aspx?Item=N82E16833704042&cm_re=gigabit_switch-_-33-704-042-_-Product
You can properly use a second router as a relay, though if not setup properly you can have addressing or other issues. Unless you need it for better wi-fi than what downstairs supports I'd stick with the switch.
I couldn't find the specs for your Modem/Router, but your "200Mb" internet sounds like the max download bandwidth from your ISP. I suspect it has a Gigibit router.
So, again, not sure where your "issue" is though if trying to copy files between computers the upstairs ROUTER could be the bottleneck if it's not Gigabit capable (one or the other, or possibly a slow-down if the 2nd router is dedicated as a relay).
*If you have a Gigabit switch any computers connected to it will share the same ethernet cable (which is fine), however they will talk to each other through the switch. They will not go through the router.
So for example if you have two upstairs computers connected to that switch and copy a file from one to the other it will go from
PC#1 -> Gb switch-> PC#2 directly.
If copying a file from upstairs PC to downstairs PC with the switch it would be:
PC(upstairs)-> Gb switch-> Modem/Router (just the ROUTER part)-> PC(downstairs)