Ping is how long it takes for information to go from your computer, to Riot's server, and back to your computer, measured in milliseconds. If your ping is in the 700's, you've got a serious problem with the overall route the data is taking. That's not a problem with your wireless router.
Ping (milliseconds) and Bandwidth (Megabits per second, or Mbps) are completely unrelated. This is most noticeable with satellite internet services, which in the best case scenarios can have a Ping of about 500-600ms, but can still offer plenty of Bandwidth - making them absolutely terrible for real-time gaming, but completely fine for streaming HD videos.
I suspect that when you say "upgraded the wifi connection" you mean you've changed to a satellite connection for your internet.