Is it possible to convert a standard WordPress gallery that I have created in a page to a NextGen Gallery? And if so, how do I do this?
Maybe someone will correct me, but I believe your answer is no. The reason I say no is because NextGen creates additional folders that contain your gallery images. It might be possible to tweak the settings to force it to use the current images location, but that would cause issues down the road if you have your Media settings as Year\Month. I used to think that NextGen was the best gallery around and recommended it to all who asked, but now I don't use it because it leaves a mess behind if you decide to use something else.