Change only file permissions in a folder and all sub-folders. (replace "your_folder" and "your_permissions" with the appropriate values).
Command:
find your_folder -type f -exec chmod your_permissions {} \;
If you only want to change the permissions for files in your_folder itself and not in its subfolders you can add -maxdepth:
find your_folder -maxdepth 1 -type f -exec chmod your_permissions {} \;
Example: find my_folder -type f -exec chmod 644 {} \;