You probably can't, depending on the model year.
For many years a trailer "vin" was simply a serial number to track production and shipping/inventory. If it has a vin and not a capacity plate, it is probably an older trailer.
Remember, tire capacity, or axle rating, does not equal load capacity.
Your best bet is to contact ez,
Contact EZ Loader boat trailers, offering custom boat trailers & adjustable boat trailers.
www.ezloader.com