At this stage, the News Feeds (RSS) module does not actually do much with an incoming feed with regards to sorting. Mostly you get the info as offerred in the feed source. The XML/XSL has some provisions for sorting that is easier to setup due to the use of parmaters which you can choose in the setup. The News module uses parameters as well, but these don't include sort order yet.
One way to achieve sorting is to create a custom xsl to do it. The caveat here is the custom xsl must be rss v2.0 compatible. Since the News modules default.xsl is compatible, we can use it as a starting point. So, copy the default.xsl to newsAsc.xsl and use your favorite text editor to add the following line under the xsl:for-each statement:
<xsl:for-each select="channel/item[position()<=$ItemsToShow or $ItemsToShow<1]">
<xsl:sort select="pubDate" order="ascending"/>
Then, save the file. You can put this file in the folder associated with your portal. For example, if this is the first portal used, it would be portal 0, and so on.
Next, when you setup the module, specify 'Other' as the news source, and then browse to your folder and file, and choose it for the transformation source.
Note, sorting by date is really troublesome if the news source is not really a valid rss v2.0 pubDate, so this may not work for every news source. You'll have to tweak it to make it work for you. This example is just one that works for me in a simple fashion, but you may need to actually create a custom template to parse the pubDate elements, then sort.