Depending on where you are connecting, it might be impossible to change (ie. some college dorms restrict that sort of thing, etc.).

However, you can try to change it in your router's settings by going into your web browser and entering 192.168.1.1 in the address bar (Note: sometimes the IP is different from 192.168.1.1, like 192.168.0.1, etc.). This should give you access to your router's settings. Every brand of router has a different set of options, but just look around and you should find an option related to NAT. In my case, NAT Redirection is located under the security tab.

Put your PS3's IP address in the DMZ server on your routers settings, it will work as it worked for me.

Or

You can alternatively use a Ethernet cable, which will make your connection much better.