Why am i lagging in mw2?

When i am playing i experience lag when i am playing mw2 on ps3. To fix the problem i bought the most expensive router and it said it was #1 best router in North America. So I tried my new router and i still lag in my game. No one else is using the internet. I got no viruses or anything. How can I fix this? Btw my router is called Linksy by cisco i think. If you know this brand how do I change bands?