How am I still lagging?

Ok so I have a HP omni120 I just got it for christmas. I also have a netgear WGR614 54 mbps router. I always used to lag or have slow internet when someone else got online at my house. So I thought a wired connection will be better, so I moved the router and modem and stuff to my room and put a ethernet from my computer to the wireless netgear router. However when my sister still gets on her computer I still get slow internet connection. Can someone give me and tips or pointers so I can make it better or should I get a new router?
 
There's an option if you log in to the router called QoS (quality of service). You can adjust this to give your machine better speed.
 
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