It has been a while since i've had to update a snap shot and being on the linux side i couldn't remember where a lot of it was.
First go to minecraft.net download minecraft.jar
choose properties and check executable.
Run the file and it will create the rest of the files by downloading them from mojang.
browse from your home folder to .minecraft. There will be a folder now bin
Open that and now take your snapshot minecraft.jar and overwrite it.
I also checked allow executing.
After that finished go to the original minecraft.jar and run with java. log in and you will see the update version there.
