ever since i moved my ps3 down a floor (its now two floors away from the wireless router) & it might also be the new firmware, fifa has been lagging like crazy for me
whats the best/affordable way to improve my connection dramatically

Affordable but maybe not possible, reposition your router.

I have my router in the basement. There were some dead spots upstairs. I moved the router 10 feet from its original position and I had a much more evenly distributed signal.

This was in an unfinished basement so I didn't have many things getting in my way when I wanted to move the router.

add a wifi only access point downstairs if you have the wiring. Set up the ssid's the same and you will have more signal through out the house. the wifi only, without router, aren't that expensive.
If you don't have a wire close, you can use those units that plug into the electrical out and send Ethernet over your power outlet to add a second WAP or even hardwire your unit. You are limited to having to have them plug into the same electrical circuit, but I am sure you can use it to help out.

Try changing the wifi channel your router uses, some channels will be better than others depending on your environment (ie if neighbours use wifi, the presence of other wireless devices such as cordless phones, cellphone towers)

You could get an external high gain antennae for your router if it has an upgrade port, pretty cheap you can pick one up for under $10. You could get a directional antennae and aim it at your PS3, but this depends where the router is positioned to make sure you can get reception to all your other devices on the network.

Is your PS3 now in a concrete basement? The probably with concrete walls and floors is the amount of metal they contain, works like a faraday cage blocking out radiation. If it were me personally I'd be inclined to run a hardwired cat5e cable to the PS3 instead.

how would i go about changing the wifi channel?

yea i would prefer to have a hardwired cable but it seems too hard to run it from the 2nd floor thru the 1st floor into the basement

http://www.engadget.com/2005/11/16/netgear-xe104-85-mbps-wall-plugged-ethernet-switch-adds-speed/

Here's what I suggest, may be too pricey for you, it's a solution to running wires and having a HARD line to you PS3.
I've used them and they work great. At 85Mbps it's faster than a WiFi.

To change you channel you need to log onto your router and go to Wireless Setting. In there you should have a drop down and a list of channels. Usually they are default at channel 6. You just have to try each one to see if you get better results. I honestly doubt this will fix your problem, instead it will be more of a temporary fix.

Even after I moved my router I still ended up going wired to take advantage of the gigabit interface.

Unlike you I only had to go through one floor and I followed a pre-existing cable run. Was actually pretty easy.