If you have internal links pointing to the page with the new/updated content Google will eventually find it, however, the quickest way to have this happen is to request a crawl in Google Webmaster Tools.
Under Crawl > Fetch as Google
Once the status of the page loads, you should see a button labeled Submit to index. Click this to submit the page to be indexed.
There are free tools available to find out the last time Google indexed (crawled) a specific page. I personally use the free SEO Book Toolbar. I believe Moz's free toolbar does this as well but I could be wrong.