You have to enter these game cheats during gameplay with Niko Bellic's mobile. When you are playing the game press up to see Niko's mobile then press up again to find the keypad and use it and that is when you can enter following cheat codes. You must enter code correctly to see the new Cheats menu option underneath options and here you can access cheats without entering the phone number again. These cheats can disable your game achievements so don't save your game after you have used these cheats.

1: To give Niko an Armer dial 3625550100.

2: If you want to restore Niko's Health use this 4825550100

3: For weapons #1 Handgun, Shotgun, MP5, M4, Sniper Rifle, RPG, Grenades, Baseball bat, use 4865550100 this number translates into GUN-555-0100.

4: To remove wanted level (Blocks "Walked free" achievement): 2675550100

5: Raise Wanted Level (Adds a star to Niko's wanted level): 2675550150, number shall translate into "COP-555-0150".

6: If you want to change weather or brightness 4685550100, number shall translate into "HOT-555-0100".

7: Spawn Annihilator: 3595550100, phone number shall translate into "FLY-555-0100".

8: Spawn Jetmax: 9385550100, number translates into "WET-555-0100"

9: Spawn NRG-900: 6255550100, number shall translate into "MBK-555-0100"

10: Spawn Sanchez: 6255550150, number shall translate into "MBK-555-0150".

11: Spawn FBI Buffalo: 2275550100, phone number shall translate into "CAR-555-0100".

12: Spawn Comet: 2275550175, phone number shall translate into "CAR-555-0142".

13: Spawn Turismo: 2275550147, number shall translate into "CAR-555-0147".

14: Spawn Cognoscenti: 2275550142, phone number shall translate into "CAR-555-0142".

15: Spawn SuperGT: 2275550168, number shall translate to "CAR-555-0168".

16: Restore Niko's Health: 4825550100 (this number shall translate to GTA-555-0100, this code also prevents Cleaned the mean streets achievements from being earned.