If you can right-click and upgroup, it is possible the background is a
separate object and you can then delete it. However, if is a jpeg, bmp, gif,
or some other raster graphic, you would need to use a separate editing
program.
Without more information (like the file type), it's hard to give much more
specific help
Yes, use the "Magic Wand" icon to define one transparent color. You don't
know where to find it? Tell us more about the PowerPoint version you are
using, the location of this icon changed.