Understand problem, but can't execute solution.

The problem: A WoAI A320 Spanair texture is improperly formatted as a 32bit BMP rather than DXT3
The Solution: Convert troublesome texture to DXT3.
But how? :-?
Current Cheap fix: The bad texture has been replaced with a good one.
The Solution: Convert troublesome texture to DXT3.
But how? :-?
Current Cheap fix: The bad texture has been replaced with a good one.