IP Address Conflict

Hi. I am at a friend's house and, even after restart, am getting a message that another device on the network is using my IP address. It says I should change my IP address. (1) Why would the conflict be occurring if DHCP is working correctly on friend's router (is it?)? (2) How do I change my IP address to resolve the problem since I don't have access to his router setup? Thanks. Michael.