This is a question I often hear from small business owners, entrepreneurs, and anyone with a personal web site. The hard part is, there is no correct answer. Here are some general guidelines I do recommend you follow in how often to update your website.
Homepage: 1-2 weeks. First, people want to know someone is actually there, not that you are a fly by night operation that failed two months ago. Even if its only a few changes to the text, updates to a ‘news’ section, or changing some images around. Secondly, Google crawls your site every few weeks to look for any kind change to the text. Google also wants to know you consistently update your pages, so this plan of every week or two ultimately helps your search engine rankings as well.
Sub Pages: 1-2 months, or as needed. Most importantly, make sure they are up to date with current prices, specials, and other offers. Again, Google likes to see changes on all your pages, so also keep that in mind.
Add New Content: 1-2 weeks. You should be adding some kind of new content, whether it be a new page or new articles, every week or so. Not only does this keep your site growing at a constant pace, but it keeps visitors coming back to see updates. This also is a plus for search engines, who will crawl deeper the more pages and articles you write for your site.
Complete Content Overhaul: 1 year. Every year, you should go back and rewrite or update the content on all *(realistically, most) of your pages. This doesn’t have to be in one day, it could strategically be over a few months. Also check for things like outdated specials, old offers, old products / discontinued services, etc.
Redesign Site: 1-3 years. Every few years, the look and feel of the internet completely changes . While in reality it is constantly evolving, a redesign every few years will make sure your web site does not look archaic or outdated. Also investigate updating any legacy software or coding you have on your site, and make sure it is compliant will all the current web standards such as W3C, etc.