I agree with the others that you need to understand the basics of image editing to make games, if for no other reason than you need to know what to as for when you have others make graphics for you and to make little tweeks when you get them.
Depending on how you came by the graphics, you may be able to ask to get them with a transparent background, or to get an alpha mask that you can use in image editor to remove the background.You may be able to get someone to make the changes for you, but it is a LOT easier if they have the original files.