ATT assigns your ip address, not the computer. You can turn the modem off and on again - and if your IP isn't static, it will assign a new ip address.
you can change the ip to the connection program. then you can put the ip manualy because the static ip sometimes has problems
Here are some ideas for changing your IP address.. Be sure to delete your Internet browser cookies before trying any. Okay, the first method of changing your ip address is obvious, but reliable. Pack up your laptop and go to an Internet cafe or public library that offers free wifi. The advantage here is that the IP change is fullproof. The disadvantage, obviously, is the inconvenience. The second method of changing your IP address is to use public proxy servers. I'm not going to cover this method here because the disadvantages are too significant. For example, public proxies are extremely difficult to find, almost impossible to find compatible with secure connections, and if they do work then there is a good chance that they were setup by criminals or law enforcement for monitoring or logging your activity. If you do want to use proxies, use a private browsing service -- they're much safer, more reliable, and offer secure ssl connection capability. One example is http://www.iprivacytools.com The third method of changing your IP address would apply if you connect to the Internet through a dialup connection. Simply disconnecting and redialing, or dialing up through another access number, will almost always give you a new IP address. For broadband cable and dsl users, some ISP's will issue a new IP address after you simply turning your modem and router off for a few hours. You'll find that when you power up again you'll get a new IP address. But not always
Unless you have a dynamic IP, you cannot change your IP. Use proxies, thats another way. As mjewel said, your IP is renewed when your connection is terminated to their exchange, and it restarts.