What are you wanting to accomplish? That is, what are your functional needs? Larger wheels mean reduced acceleration and reduced torque to the ground (due to a higher final drive): there are
If you go taller then you'll likely need to go with higher ply ratings (especially for loads). Keep in mind that it might be a struggle to mount higher ply tires on some rims: I have no specific knowledge of these rims (or anything else on small vehicles like this). Increased sidewall height might also cause clearance issues.
You can probably figure out how much width that you can get away with by just doing full turn-stops and checking how much clearance you have. There are things like wheel spacers and offset rims, though I don't know what exists (and is safe) for these vehicles.
I have a curiosity about utilizing wider tires as I suspect I may need more flotation.
Be sure to keep the same ratios front to rear as is for stock otherwise you can mess up your 4wd.