how to increase API Level in android for already created project

[shawn peter]

I have created my project for 10.Anyway i need to increase it to 11 now as i need to use Holo Dark them.
1)How to increase already created project API level?
2)can we use Holo Darck thems for API 11 below projects?

[Ulf Dittmer]

For an Ant build you might have to adjust project.properties; other build systems probably have some other way. And, of course, you need appropriate minSdkVersion and targetSdkVersion values in AndroidManifest.xml.

This answers your second question: http://android-developers.blogspot.de/2012/01/holo-everywhere.html. If you haven't worked with styles and themes before you should also read the "Styles and Themes" page linked in there.