Use a VPN. I recommend Hotspot Shield.
If your internet connection has a dynamic IP just turn the router off and you should get a different IP when it reconnects.
Static IP you'd be best with a proxy or VPN.
1. You can't. Actually that's not entirely true, but see #2.
2. If the site IP-banned you, you obviously did something really nasty to deserve it, so why should we help you get around this?
Download and install Windscibe.
It's free and will allow you 10 gb of free and safe internet access every month (you just need to provide them with an email address) otherwise you only get 2gb!
You can use a Proxy,VPN or Tor for this.
use an vpn or proxy site
you can use vpn server
IP address banning is very rarely used. If you have a portable device such as a tablet, phone or laptop, go to a coffee shop or burger joint and buy something. While you consume your purchase, try accessing the site. You are guaranteed to be using a different IP address as it is a different ISP connection. If you are still banned, then this confirms it's not an IP address ban.
Banning can be through the account username, a cookie or marker on your device, your device's serial number or even a credit card number.
Hotspot Shield, it wont show your IP address