-Right click the shortcut icon for the game and choose properties.
-Click on "Find target..." button and you will be directed to the 
 folder of the game.
-Double click on the folder "levels" to go into it.
-Inside the folder "data", there is a file called settings.xml. 
-Right click on it and choose to open with notepad.
-Once open, scroll down until you meet a line which starts with
 <Costs>. Here is the list of the costs of all the upgrades.
 i.e. Shop_1 cost_0="0" cost_1="0" cost_2="0" cost_3="0" means that
 the upgrade for the first upgrade is always free.
-The easiest way to edit is to use "CTRL" "F" on your keyboard and 
 find the word costs to go there.
-After finishing, close the file and save it. 
- Now, all the items in the store will cost what you have changed.