Remove the latch. Use a wire brush to take off as must rust as possible and scrape any flakes that don't brush off. (Like Bar-B-Que brushes, some wire brushes have a cheap scraper on the end) Lightly sand the remainder enough to take the gloss off. Clean well with alcohol or mineral spirits. Paint rusty areas from a can of rust reformer and let dry according to directions. Spray paint with a new coat of white paint. Recoat as necessary. Reinstall.
Save the cans so you can do it again in a few more years.
I used a stock Rust-Oleum white paint to do my latches a second time before I sold the Niagara, but no longer have the can. Take one along with you to pick out the correct white. Unless you can sand blast, the use of rust reformer is crucial for the longest lasting job.
OTOH, you can buy whole latches on E-Bay for three bucks each plus six for shipping