The OP is using a Mac. There is a GIMP version for Mac, but the other two seem to be windows only. The OP would need to buy and install Windows on his computer.
Oopss.. pretty windows centric here... lol! I missed that... I know the Mac's have very limited software choices... unfortunately! So many mac users run windows anyway...
Yea, my experience with computers is rather limited. Years ago, we had Macintosh, back in the 80's, but then we had to learn Windows computers for work.
Then, when I was considering photo editing, I asked some guy at a big-box electronics store what I need, and he said "Apple". I like the large display on my iMac, but I am limited on software choices.
I bought a CADD software, and Aperture, and several cheap applications, and found a few free ones.