There have been several posts concerning replacing 13 inch trailer wheels with 14 inch and concerns what tire spec would fit under the fenders. I found these charts and thought they would provide a good reference.
Find your existing 13 inch wheel tire spec on this chart to determine the outside diameter of the tire.
Measure the clearance between your existing tire and fender to determine the max tire diameter you can use then find that diameter on this chart. Select from the options under the tire diameter based on the width of your desired 14 inch rim.