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I assume you are talking about the lines from the pole into the conduit that leads to the service panel, correct? If so, then you should contact the utility company that they may not meet present-day codes and they should replace them at no charge.

If you mean the lines inside the conduit that feed the panel, then that is your problem and it can easily be remedied by an electrician who will feed larger lines to the panel.

If you service lines are truly too small, then you could see the symptoms you describe, especially dimming lights when heavy draw appliances are being used. If you suspect such, call out an electrician to check the amperage/voltage drops through out the house. Too small of wiring can overheat under load and that is something you don't want to happen.