When posting asking for help, it is helpful for those wanting to help, if you would follow some simple guidelines:
1. Give the module version you are using
2. Give the DNN version you are using
3. State if this is a pubic hosted install or a local install
Now, since you don't state any of the above, I'll give you the two possibilities, that I see most often.
Using, News module v4.0.x:
There is an option in the Module Settings area that allows you to choose how many items to display. Its default value is -1, which the programming method uses as meaning 'display all avaliable'. Any other positive value can be entered. If you are using this module to render aggregate feeds, remember that only the specified number of entries are used for the total number of entries retreived, which means if your first feed has 20 items, and your second feed has 30, and you specify the module to show 15 items, the first 15 items from the first feed are going to display, not the the first 15 from each feed. Buggy? Yeah, but that's the way it works now.
Using the News module v3.0.x:
You have to create a custom XSL and add a bit of code to limit the number of items. Save the file and upload to your web site. Then, you would specify that file as your XSL transformation file. You need to know a bit about coding XSL to do it, and understand it, though.
The code snippet to limit the items selected to the first 5 items looks something like this:
<xsl:template match="item">
<xsl:if test="position() < 6">
<!-- your code here -->
</xsl:if>
If you need the full xsl, search my posts, I'm sure I've given it out several times. You could google it too, as others have posted the info, as well.