HELP WITH TILES - MAKING TRANSPARENT BACKGROUNDS

I really got into the idea of making a chips game and recently just
finished acquiring the tile sets I'll need by taking screen shots
and resizing them. But I'm not very good at using image editing software.
I was wondering if someone could make some of the backgrounds of these transparent.
Here is the set. Below it I will tell you which one I need done.


Gate, Chip, all keys, all shoes, monsters, chip character.
(The spaceship, bug, and tank only need to be done once
since they are all the same image rotated.)

That was pretty fast, I knew someone would know how to do that faster than me.
Thanks for the help!