I am having a problem while gaming on my new android update on moto g (2nd gen). So, i want to downgrade the android version please help me out.
A downgrade (as well as an upgrade) can be performed by flashing the corresponding ROM that match your device configuration, that is MOTO-G (2nd Gen.)
So, first thing is to find Appropriate ROM for your device MOTO-G.(2nd Gen.)
You may find more hints at this LINK.
Once you find the ROM, you can downgrade(or upgrade), as needed.
Refer rom-flashing for more details and instructions related to ROM Flashing.