Should I Update Old Posts or Write New Ones for Better SEO ?

My old blog posts get very little traffic. Is it better to update them or focus on writing new content ?

They have gained some age, so it's always better to update. Unless they are completely crap, in that case, study the topic of "content pruning".

As a priority, try to update the old post with some recent data and information if its doesnt work as you expected then post a fresh new article

If the old posts are already indexed, I’d usually start by improving a few of the strongest ones first refresh the content, tighten the structure, and make sure they’re still relevant. At the same time, keep publishing new content so your site keeps growing and signals activity. A mix of both tends to work better than focusing on just one side.