Welcome to the Bunnings Workshop community @davisfamily12. It's amazing to have you join us, and many thanks for your question about removing varnish.
You can either chemically remove it with paint & varnish stripper or abraid it off with sandpaper and a scraper. Depending on the thickness and how degraded the varnish is, you might need to employ a couple of methods. If you're going to sand the varnish off, I'd highly suggest you invest in a random orbital sander which will be much easier than doing it by hand. If you'd like to post an image of the table, our helpful members will better understand what methods they can suggest.