May lawn has about 2" more dirt under it that I would like. What is the best way to lower the level of a yard? I was thinking of aerating and then removing the plugs so they didn't breakdown back into the lawn. Maybe doing that 5-6 times might do it? I've heard that you should only core aerate every 2-3 years or so, but how frequently could I do it without hurting my lawn? Anyone had any experience with this? Is there another technique I should consider?

Outside of removing the turf and physically removing the unwanted soil, I have never, personally or professonally been asked that question. Sounds like a grading issue, that type of large equipment may help your cause. However, aerating your lawn will not accomplish your goal. In addition, aerating is the healthiest thing you can o to your lawn all year, besides keeping it properly fertilized. An annual aeration, in no way, will harm your lawn; in fact, you'll make it healthier by reducing the thatch layer and improving the flow of air, water, and nutrients to the root zone.