hi every body;I want to know where is the parameter to change the k2 image alignment in articles or categories?Like: left, right, center,...

If you investigate the attached png from K2Joom.com you will see that he is doing it with css styling. I think he is using first custom K2 template and second css4K2 to accomplish this without changing the K2.css file in the core. This is the best way unless you want your entire site to do one thing, and you also want to make the changes again.
Firebug is your friend!