There are many ways to change your IP addresses in order to get a large number of voters in a certain contests. But several methods will work only in your computer but may not work in someone else and vice verse. The IP address is a logical address give to a network card in command to set up communication to identify the computer and the network.
Based on certain rules and regulations the network administrators regularly assign IP addresses. Also try go to your internet provider to help you guide change your IP address. Or simply watch this video on YouTube that might help you.
If you are referring to the physical IP address of the computer, yes it is possible but it only applies to the network or local area network where the computer is currently connected to. But if you are referring to the IP address of the computer on the internet, literally, this is not possible because it is your ISP who assigns the IP address to you.
If you are using a DHCP connection, which most of the ISPs use nowadays, your IP address changes over time. But there is a way how to change your IP address on the internet using proxy or VPN. With a VPN or virtual private network, you can select different servers each time you connect and each server use different IP address.
When you are using a proxy or VPN, your current location appears as if you are located in a different country and state. This allows you to bypass any blocked websites in your country.