As often as it makes sense. At least two or three times a year, but preferably more often.
Google rewards websites that add fresh content (blogs, press releases, new product pages) because it shows you’re investing in your website and keeping it current.
More content helps establish you as an authority on a subject and makes your website a better destination for visitors.
But quality trumps quantity. So focus on creating content that offers value, not just keyword-stuffed SEO fluff.