Can I change icon for an app and how? I have XAMPP on my Mac with El Capitan and the icon is strange and I don't like it. It is not the same one as I am used to, on my other computer running WIndows. How can I change it?
You can edit any icon by right-clicking (control-clicking) the application, choosing Get Info, and dragging the replacement icon over the original icon at the top of the window that appears.

You can also copy and paste the image you'd like to use as an icon, as mentioned in Apple's documentation.

This works for files or folders you'd like to change the icon for.