Hi Melvin, if you update your article a higher time Google crawls your site it’ll notice a change from the last time and re index the page. Changing the ‘Published On’ date is simply another indicator to the Google crawl. But for readers of your blog, this may help them see you’ve made some changes. So, ideally update both so it’s clear to Google and your readers that you’ve updates the content. The only caveat is this might be for massive adjustments to the content.
For instance, if you only update a spelling mistake then there’s no are looking to change ‘Published On’ date.