Hm, I don't know why the designer would give you a .PNG image but not use a transparent background. If the white background is the problem it's easy to get rid of.
Even with the PSD you won't be able to make it any bigger easily. You'll be able to resize the text but the custom "O" will be distorted.
If you want to get a logo that you can resize just by dragging the corners you need someone to create one in vector format using CorelDraw, or Adobe Illustrator.
PM me with specifications/examples.i am looking for 3 banners. do reply me