Way to lower ping in Minecraft? Should I change internet?

Hi, i'm australian, and I get really bad lag, and I have 51 download speed and 2 upload speed, when I connect to a server, I get so much lag, my computer is windows and is 3 years old, or 2, will CCleaner help with the lag? I'm not talking about FPS lag i'm talking about server lag ping/ms. I've seen things like cleaning the computer with CCLeaner and then installing gamebooster, will that work? Also i'm with bigpond in Australia, should I change to a different one? Which one is best in Australia for gaming? Broadband?

High ping generally just means you're too far away from the server you're connected to, though a server could also (rarely) be overloaded. That's not something you can easily resolve, short of physically moving closer to where the server is at. You can try killing off programs and processes that are using bandwidth (torrent clients come to mind), but that is unlikely to matter much unless something is running your connection dry.

As for the programs you mentioned… CCleaner probably won't do much, and Game Booster (been a while!) I believe mostly helps with FPS issues. I'm not familiar with Australian ISPs, so somebody else may have to chime in there.

CCleaner won't help with network lag. It does help with overall computer response, keeping files clean, but nothing to do with networking.
Gaming lag from a server is usually a couple of things. First, distance to the server. Your gaming packets have to go through a lot of internet providers. Some may be slower than others. Some may be using satellite links to other parts of the world. Satellite alone will add about 200-300ms lag to any gaming traffic.
Second the server may be busy, or has poor upload speeds. Other players would see the same result in that case.
Next, your own PC. Is it up to playing that game ok, or if the video card low end? Is the CPU a slower speed CPU? In MC, the game runs on Java, basically an interpreter type of program (very slow compared to compiled code). MC needs enough CPU power to run the game properly. A computer 2 or 3 years old does not say anything about the speed of your system, it could be a low end 1 or 1.3Ghz dual CPU or a high end 8 core 3.4Ghz system - can't guess…
Finally, are you playing over wireless? If so, try playing wired to the router. Wireless produces a lot of lag.