No need to change rims to run higher load range tires. From the Carlisle Tire site:
"What is the maximum psi limitation for your trailer wheels? Max air capacities are typically a function of the tire, not the wheel. Unlike tires, the load rating of a wheel is not generally dependent on the operating pressure. The wheels themselves are manufactured and tested to a load rating (without consideration of pressure) and can safely support that load. As long as the load is within the limits of our wheel's load rating in pounds, our product will perform as expected."