I have a picture that I put in my project and it doesn't cover up the whole screen (it leaves black bars). How do I make the picture cover it without editing the whole track? I only want to affect this picture. I know I can enlarge the whole track, but that would affect all the other pictures on the same track. Thanks in advance!
Go to the pan and crop tool on the picture, and on the Preset drop down on the top of the window select (or create) whichever aspect ratio is what your project is. For a lot of people it's 16:9. Just know that you'll cut off some of the picture by doing this since you still can't change the shape of the picture itself, so you have to be ok with cutting off the ends of the picture and possibly re-framing it.
You can right-click on the window in Pan/Crop and select Match Output Aspect and it will match the crop to whatever aspect your project uses without you even having to know what it is (or changing it).