From b2evolution manual

The Smilies Plugin provides a toolbar for the "Write" tab, which every user can disable and replaces the text smilies (e.g. :)) when the item gets displayed with the "Smileys" renderer activated for it.

[edit] Location

The Smilies Plugin gets shipped with b2evolution and can be found in /blogs/plugins/_smilies.plugin.php.

[edit] Adding Smilies

You can add new smiley images by uploading the images to the rsc/smilies/ folder. Then you will have to edit the smilies plugin. The list of smileys [one per line] is in the format : char_sequence image_file // optional comment To disable a smiley, just add one or more spaces to the start of its setting