There are two options. The first (and better) one is using the Fetch as Google option in Webmaster Tools. Here are detailed instructions:

1. Go to: https://www.google.com/webmasters/tools/ and log in
2. If you haven't already, add and verify the site with the "Add a Site" button
3. Click on the site name for the one you want to manage
4. Click Crawl -> Fetch as Google
5. Optional: if you want to do a specific page only, type in the URL
6. Click Fetch
7. Click Submit to Index
8. Select either "URL" or "URL and its direct links"
9. Click OK and you're done.

With the option above, as long as every page can be reached from some link on the initial page or a page that it links to, Google should recrawl the whole thing. If you want to explicitly tell it a list of pages to crawl on the domain, you can follow the directions to submit a sitemap.

Your second (and generally slower) option is, submitting urls here: http://www.google.com/addurl/