How do I change a price on a royal snapple vending machine from 1.50 to 1.00 its the older model

I am looking to change a price on my snapple machine it has 8 sellections and one of the 8 is set at 1.50....I want to change the price to 1.00, but I have no clue on how to do it. I open the machine and found a button to push...when I push it the display screen shows (cp). I guess that merans change price. I tried every which way possible.....I realy need some help with this...

have you tried to push the actual soda buttons outside. Once you push the selection (coke) hold it until desired price is showing. If you release the button it will go higher and if you push it again it will go lower or vice versa.