The answer to 'how to test panel upgrade' is to first turn off the main breaker to the electrical panel. Then, use a voltage tester to check that the panel is de-energized and safe to work on. Next, remove the panel cover and visually inspect the condition of the breakers, wiring, and other components. If everything looks good, you can proceed with testing individual breakers by turning them off and on to ensure they're functioning properly.
It's important to take safety precautions when working with electrical panels, such as wearing rubber-soled shoes, using insulated tools, and having a helper present. If you're not comfortable performing these tests or notice any issues, it's best to call a licensed electrician to inspect and upgrade the panel as needed.