You won't be able to unless you leave your router off for a few hours and power it back on. The IPs are dynamically assigned, and someone else could very well have it. It's a luck of the draw.
The best way to handle such a situation is to handle access not by IP address, but by encryption keys and passphrases that are hard to brute force. If your IP must remain the same, consider getting FiOS Small Business service with a Static IP.