You can change a button's size only if there are no images in the button. If there are images, then the button's/panel's size is controlled by the image size. You will need to save the images to the hard disk, edit, and reload them to change the size.

You will find that you will most likely need to pick up image editing as well to develop really nice looking PCFs. Some of us use Paintshop Pro, some use Photoshop, some use CorelDraw, other use GIMP, LviewPro, or MSPaint.exe. Different tools have diffenrent complexities and different prices as well as features.