Without upgrading the head unit, the cheapest and simplest upgrade for you from your stock speakers is to upgrade to a decent component set ( 6.5inch mids + tweeters). Dont get coaxial set you wont get much gain from the effort.
Budget around 200-500 should be good enough.

Be aware that there would be installation charges by ICE shops, wiring, and speakers mounts if required.

Go with this setup, if itchy and want more only add the rest.