Are you going through a router? If so you can assign yourself a static ip address, but if you are directly connected to your dsl/cable modem then no you are on a lease and calling them and asking your isp will not change it due to. many reasons, Bittorrent downloads, MP3 downloads and bandwith usages.
I don't think she/he wants to change LAN IP. That doesn't make any sense... you don't need a new LAN IP very often.
99% of the time, the easiest way to change your WAN (external) IP is to unplug the cable modem or DSL modem from the power supply and wait a few minutes, then plug it back in. Chances are, it will usually come back with a different IP than it used to have. After it's done rebooting, you can use....