Normally in Kunene, the module which manages Forums under Joomla when you click on "My Profile" there is a menu to edit your profile. The third item on the menu is "My Avatar".
Recent releases of Kunene have been broken, although this is fixed in the latest release.
" Kunena 1.5.11 Maintenance Release
The Kunena Team announces the immediate availability of Kunena 1.5.11. All users are recommended to upgrade to this maintenance release.
Kunena 1.5.11 fixes one major bug in Kunena 1.5.10, which prevented all users from getting subscription emails.
This release also contains 30+ bug fixes which were made for Kunena 1.5.10. They fix various issues reported by users and moderators recent months. This includes fixing a regresion with avatar uploads or when choosing an avatar from the gallery. "