Menu on PCD8544 controlled by IR remote

Hello guys! I have a problem in interfacing a PCD8544 display with an IR remote. The actual problem is, I want to control some sort of menu on the display using the IR remote control instead of those 4 physical buttons that are supposed to be connected to digital pins of Arduino. When Arduino is receiving the correct code from IR it should emulate the physical pushed button as HIGH value. How should I do this? I'm using this sketch Tutorial: come gestire menu e display LCD con Arduino – Coagula – Giuseppe Di Cillo for the menu.

Please help me! I'm a bit n00by in programing so I need your advices. Thanks!