Kenmore 16223 - hard to light, not heating enough

Question

We're renting an apartment that came with a Kenmore 16223 grill. The grill doesn't light easily or achieve high temperatures. The highest it will go is 275. It is also very, very dirty. We assume that the problem is that it needs to be cleaned, and possibly that it could use more propane (although the tank doesn't appear to be empty). Please advise on best way to clean the Kenmore grill, and what other "diagnosis" there might be for the difficulty in lighting and achieving a high temperature. Thanks in advance!