It'll ask to auto-update if you've legitmately bought it and using the actual client.
If using a pirated one which I won't blame you for since I did that in the beginning as well; check force update and it'll update.
If you mean inserting a new 'snapshot' patch; those are test releases.
To install these, you've got to go to the .minecraft folder by going to %appdata% in the 'Run' window.
I'm bad at explaining this but if you google 'how to find the 'appdata' folder for minecraft' or something like that I'm sure you can figure out how to reach that folder. Make a shortcut when you're there.
Then simply insert the latest snapshot, downloadable at the forums, and then insert that in the %appdata%/.minecraft/bin/ folder.
It's 4 am. I'm sorry for being vague.
Good luck anyway.
One question,whats the point of updating a cracked version for new stuff? You want new stuff, buy the game like most people here. Not trying to be rude or anything, but I just find it stupid that people don't have $25 to spend on a game, so they get it pirated.
I dont think the problem is the money its how to get to spend it. Like im just going to say that alot of the Minecraft users are 8 - 14 kids around these ages dont usualy have a credit card or paypal or anything and im going to say that if a kid asks his parents if he can buy this game with there credit card the parents going to say NO! Thats why i would like to see it sold in shops. But then they would have to set up a serial type of regestration thing and yeah. But theres allways going to be people who want to pirate but dont see the point of pirating something thats $20 EURO, well $32 NZD i think it was for me. Still not that much.