Can I change my ip address?

Your IP address depends on your ISP. If it's static, it won't change. Most residential connections have dynamic IP addresses. You can try turning off your modem/router for a few hours (eg, overnight) and connecting them again, which may force a new IP address.

Matt

Your IP address is determined by your ISP service provider. You are given an IP address by your ISP when you (your computer or your router) logon to their network. This is called DHCP. You can try powering cycling your DSL or Cable modem and see if it gives you a new IP address. You have no direct control over this process however. Your ISP does.

The IP address is set by your internet service provider, and, unless you pay extra for a fixed address, may change at any time, or be assigned to someone else, but there is no way for you to make it change. What sort of a website would rely upon user IP addresses. Try using another computer, such as at an internet cafe, to set up an account at the website.

The public IP address is shown at sites like:
http://whatismyipaddress.com

It can be easily forced to change on Asymmetric Digital Subscriber Line (ADSL) or Fiber To The Home (FTTH) just applying the settings at the router control web site:
http://192.168.1.1

or turning off/on the router or resetting the router.

The problem arises with coaxial cable (Data Over Cable Service Interface Specification; DOCSIS) or coaxial-cable-fiber (Hybrid Fibre-Coaxial; HFC), in which case only the ISP can easily change such IP. In such cases it is possible for the user to change the public IP address, but it requires to transform the router-cable into a router-modem (which can connect a single Mac) and then add a neutral router (to have more than one Mac on the network, or a Mac and ethernet printer, etc).