speakers

Hi all! I've owned my Swift for a couple of months now and loving it so far! I just want to upgrade the speakers and didn't know if anyone here has done so and knows the sizing? Thanks! 🙂

I thought the sound was rubbish so i changed head unit for aftermarket stereo even though sound is better its still not good enough so i think i need to change the speakers, can anyone suggest good speakers and what size i need ?