how do i get all my images to one size

I have images on my site that i know are well big enough to fit in the given space but the size keep sputting them up smaller.

Now i know how to adjust the over all size of the images through the admin setting and ive done so.

Some pictures take up the space as needed but others only take up maybe a 3rd of the white space.

Now i know when you go in your products and upload an image into a product

that it will generate its own image to fit it but its not generating them big enough even though i know they are

capable of doing so.

Even when i go into the product and delete the thumbnail picture, it doesnt change.

Can someone help me here and tell me why the images wont get bigger?