1. Connect your Action Replay to your computer using the provided USB cable.
2. Open the Action Replay software on your computer.
3. Select the "Codes" tab.
4. Click the "Add" button and select the ".ar" file containing the codes you want to use.
5. Select the codes you want to use from the list and click the "Add" button.
6. Click the "Save" button to save the codes to your Action Replay.
7. Disconnect your Action Replay from your computer and connect it to your Game Boy Advance or Nintendo DS.
8. Turn on your Game Boy Advance or Nintendo DS and start the Pokemon FireRed game.
9. Press the "L" and "R" buttons simultaneously to open the Action Replay menu.
10. Select the "Codes" option from the menu.
11. Select the codes you want to use and press the "A" button to activate them.
12. Close the Action Replay menu and continue playing the game.
Note: Not all codes will work with every version of the game. If you are using a modified version of the game, you may need to use different codes. You can find codes for Pokemon FireRed online or in gaming magazines.