You do not say the age etc, you only really need to repaint it if you are starting to get corrosion issues, is it new? is it corrosion proofed, ie internally painted? Most corrosion will form underneath from standing in wet grass etc and also rain will run off the top and then hang on the skin joints, this can wick into them if the paint is cracked.
I reskinned a "new" 2005 Piper Archer 3 that was "corrosion proofed" well all bar one skin in the tail which for some strange reason was bare metal.. another thing noted was although corrosion proofed as we pulled a damaged wing skin to replace it, there was NO paint on the skin where they overlapped, the one place corrosion tends to form.
Best treatment in my mind is ACF 50 or similar, this is sprayed internally in the structure and protects it, it also seeps into the skin joins protecting them.
ACF-50 and Corrosion Block total Corrosion Control
This will help you understand corrosion and how to protect against it. Keep the drain holes clear, keep it clean and waxed and you are ahead of the game compared to some.
https://www.faa.gov/documentLibrary/.../AC_43-4a_.pdf