NVIDIA Texture Tools or the Intel Texture Works plugin for Adobe Photoshop.
In most modern games, loose .dds files should be placed in a specific subdirectory within your game's Data folder (e.g., Data/Textures/Interface/ ). Download Main Dialog2 dds
Free tools like or Paint.NET also have native or plugin-based support for .dds files. NVIDIA Texture Tools or the Intel Texture Works
If your modified dialog box isn't showing up, ensure the image dimensions are a power of two (e.g., 512x512 or 1024x1024), as many engines will fail to load textures that don't meet this rule. 512x512 or 1024x1024)