How to center the icons…?

From the FAQ:

How can I align the sharing button(s) to the center or to the right side of posts?

It depends on your theme, but you can try adding the following CSS code to your main stylesheet.

To align right:
.addtoany_share_save_container { text-align:right; }

To align center:
.addtoany_share_save_container { text-align:center; }