All of those suggestions are fine, and if you want to make your own icons some of those are programs that do it, but it's REALLY easy to just change an icon with another icon that you already have (in the correct format). It's just copy and paste. If you want to take the icon from one file and put it on another do "get info" on both and click on the icon you want to copy so it's surrounded by a blue border, click apple+c, then go to the other window and click on the icon so it's highlighted, and apple+v. If you have an icon file (.icns) you can just click on the file and do apple+c and then paste it the same way. Once you start messing around with icons you will probably want to start making some yourself (at least if you're into doing graphics on your computer) then you'll need a program to convert your image files into icon files. I use img2icon just cause it's really simple and easy... no extra functions I would never use, just drag the picture over the indicated spot and drop, and it'll convert it to .icns and put it where you specify.