Instructions
Download a texture installation file for an aircraft that is already loaded in to your Microsoft Flight Simulator X game.
Double-click the downloaded installation file. If the file is a self-extracting EXE file, type in a location to temporarily extract the file to at the prompt. If the file is a ZIP file, click the "Extract All" button and specify a temporary extraction folder.
Open the folder that you extracted the files to in a Windows Explorer browser window.
Open a second Windows Explorer browser window and navigate to the C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\Airplanes folder.
Double-click the folder that corresponds to the airplane whose texture files you would like to replace.
Locate the Texture subfolders in the airplane's folder. Right-click each Texture folder, click rename and change the name to oldTexture or a similar name. You can later rename these folders to their original name if you want to reinstall the old texture files.
Click the temporary file folder that you created, then click and drag all Texture subfolders to the airplane subfolder in the other Explorer window.
Run the Microsoft Flight Simulator X game. The airplane that you edited now features the new texture.