Hi Friends. what is this part back on a 6v DC motor of my kids ride on bike (1st pic attached). i need to replace this with 12v motor now. Do i need to change the motor only or including this circuit? this circuit come along with motor itleslf or i have to buy separately. Thanks in advance

 

Why do you need to replace the motor? Have you changed the battery for a 12V one? Are there any electronic circuits controlling the motor? If so, they will also need to be replaced.
The circuit board on the back of the motor looks like a simple non-active noise suppression circuit. If you increase the battery voltage to 12V, the black capacitor on that board must have a rating of at least 16VDC.

 

Why do you need to replace the motor? Have you changed the battery for a 12V one? Are there any electronic circuits controlling the motor? If so, they will also need to be replaced.
The circuit board on the back of the motor looks like a simple non-active noise suppression circuit. If you increase the battery voltage to 12V, the black capacitor on that board must have a rating of at least 16VDC.

Many Thanks KeithWalker. i wana increase the speed of bike. i already bought a 12 v controller and another 6 v battery to put in series to make 12v. but the motor i bought dont have this circut (noise suppression). i can attach the motor without this circuit? is it safe?

 

It will probably work without the noise suppression circuit but may not be reliable. The two yellow capacitors on the circuit board are 0.1uF disc ceramic capacitors. Take these off the board, or use new ones and connect one from each motor input terminal to the metal case of the motor.