A surefire way to get a speed boost out of your old, underpowered phone is to overclock it. We've also discussed this already before, so we won't get too deep into it here, but I will remind you that to overclock, you'll need to install a custom kernel. These are specific to your device, so you'll have to do some googling for compatible overclocking kernels to find one that's right for you. Generally, kernels are organized by two things: voltage and clock speed. The higher clock speed you choose, the more likely you'll need a higher voltage kernel (which, by the way, will drain battery faster). As long as you're not going overboard with the overclocking, you should be able to get by with a low or standard voltage kernel without a problem.
source lifehacker.com