If you're looking for the link to do it, you need to click the "User CP" link near the top left of the screen. The "Edit Avatar" link is in the list of links on the left side of the screen - you'll find everything you need after you click that link.
Is that what you were looking for?
EDIT: Also (if you haven't already), check out the
Beginner's Guide to LO - it has a lot of useful info (
link).