Doesn't have to be for 30 minutes, you may be able to just turn it off or reset it and it can change.
You can tell by typing "My ip" in your web browser and see if it changed. If not you may have a static ip which you are unable to change.
If you ring up you're internet service provider they might be able to change you're ip but in most cases they can't if you have a static ip unless you change you internet plan.