how to change speed animation at run-time?

i have a list sprites in drawable folder. One xml file with:

PHP:

1.  
2. <?xml version="1.0" encoding="utf-8"?>
3. <animation-list xmlns:android="http://schemas.android.com/apk/res/android" >
4.     <item android:drawable="@drawable/fire_00000" android:duration="400" />
5.     <item...

how to change speed animation at run-time?