In this case you have one of two options: First, you can edit what you already have and erase the white bits manually so that they will disappear as the way some images work, I assume you cleared by selecting the white and removing it. What you would want to do then is clean up the area around where you erased and the white bits should be gone. Second, you can start over and save your file as a PNG the first time around. Be sure to erase the area you want and make sure you have the Alpha Channel Enable before you erase anything. Let me know if you have any other questions.