No, you can't change it. Also, neon_duke is not necessarily right when he says it's static. Static public IP addresses are rare and expensive, so it's not likely that you've got one on a domestic cable service, unless you're paying for it.
Cable internet addresses, like dial-up ones, tend to be assigned upon connection. This address is obtained from the DHCP (Dynamic Host Configuration Protocol) server when the device connected to the cable modem connects. Each DHCP lease has a specific length of time attached to it, which is usually in the 24-48hr range. Once the lease expires, if the computer is still connected to the cable modem, another lease is sought, and this will usually be the same address, because DHCP servers and clients develop an 'affinity'.
Obviously, Jordan is right, in that you should try not to get your IP address banned!
Oh, and this is a computing question, so I'm going to wing it across to the Computers & Electronics forum.