You can use any decking cleaner or multi-purpose outdoor cleaner that you have left over from cleaning your deck to clean your fence.
Use your outdoor cleaner to mix water with it in a bucket, according to the directions on the bottle. Or use it as a garden sprayer.
Spray the mixture on and then brush the mixture in well.
Allow the cleaner to rest on the fence for approximately 5-10 minutes in order to do its job.
You can then rinse the fence off with a hose, or you can use a bucket full of water and a sponge to thoroughly rinse it.