Before upgrading a CPU in a laptop you need to know if the CPU can even be removed. Many laptop manufacturers solder a CPU to the motherboard making it virtually impossible to replace without advanced knowledge and equipment.
If it can be swapped out, you would need to find a processor of the same socket. The A4 7210 is a Puma+ processor using the BGA (FP4) socket. You may be able to swap it out with an A6 7310 provided your CPU is removable.
Keep in mind that laptops are tuned to work as they are built and adding beefier specs will increase power consumption and reduce your battery life. You may also experience increased temperatures. Tread carefully!