Treating frogs for parasites can be very tricky. Many products that are available for fish and reptiles don't do well on amphibians. The reason is that their smooth skin absorbs chemicals more quickly causing harm.The first thing you need to do is identify the parasites. You can probably tell if you look at the skin carefully with a magnifying glass or check a fecal sample through a microscope. You can easily find information about parasites from the web. Here is a link that might help: AMPHIBIAN PARASITE OBSERVATORY
A biology teacher at a high school or college may be able to offer some assistance.