Game Collision some Logic and files.

I have the following images created
“2bananaMonkey.png” “2bananaGorilla.png” – each has 2 bananas
“1bananaMonkey.png” “1bananaGorilla.png” – each has 1 banana

each gorilla and monkey holding 1 or 2 bananas.
how do I create a collision so that when a gorilla touches “2bananaMonkey” it switches the image to 1bananaMonkey showing the monkey lost a banana and inversely when the monkey collides with the gorilla but the switch only happens when a specific body part of the monkey/gorilla touch the banana not just when they collide.
Could anyone help me out with this?

I am looking at some examples and I see files like “ui.lua” “build.settings” “director.lua” “config.lua”. For what I know with Lua I am only familiar with putting everything in “main.lua” could someone give some more insight on those first ones, I realize the “build.settings” is used for orientation , how can I set up “config.lua” to run on
iPad: 1024x768px, 132 ppi
iPhone/iPod Touch: 320x480px, 163 ppi
iPhone 4: 960x640px, 326 ppi
and which is a good resolution/dimension for the created images in order to run smoothly on all systems. Are there some specific files to include in a Corona app? [import]uid: 43696 topic_id: 7673 reply_id: 307673[/import]