In the town touch the door of one of the 3 buildings and a menu will pop up. Move the cursor with the arrows and select with the space bar. The items you can upgrade and the price is displayed in the menu. Your gold is displayed at the upper right hand corner of the screen and you will see that number decrease as you buy upgrades in the town
 "fatspliffs"){kind=icon}
 "bryser1"){kind=small}