Hi Sheryl,
While there's no particular way to submit a single page, afetr all, the trouble is that the page is already in Google (but with oldish content), there are a few ways to achieve this.
1) Getting the cache of that page removed in Google.
When you change the page, you can add a robots meta tag specifying "NOARCHIVE" to it.
Then you can request cache removal for that, from your Webmaster Tools account.
2) Getting the page recrawled and thus recached, faster. This will depend on how often this page gets recrawled in general. You can always post some links to it on pages that are likely to get crawled more often.
3) Prepare a fresh sitemap and resubmit it. Make sure that url is in the sitemap.
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