You need the wheel/tire combo that fits your trailer hubs.Your fenders should be fine.They may need to be raised a little.Just make some brackets out of 1 inch angle steel/iron to raise them up a couple inches.That should be it.Boat bunks may need to be raised a couple inches.
Your ride may be a little softer (bouncier if it is a light boat/trailer) but your bearings and tires will thank you for the upsize.
The part about loading/unloading can happen but it will only raise you 2". Most trailer bunks can be lowered accordingly to get your boat back to the original ground clearance.