Facepunch.Steamworks Wiki

Editing Workshop Items

Editing a file is exactly the same API as creating one.. you just need to get an editor for it.

var result = await new Ugc.Editor( fileid ) .WithTitle( "My New Title" ) .WithChangeLog( "Changed Title" ) .SubmitAsync();

You only have to change the parts you want to change, and can even include a changelog.