Fatal error after updating to wordpress 4.2.2

I tried updating my wordpress to the latestt release being version 4.2.2 but after that immediately it gave me this error message:

Fatal error: Cannot redeclare get_avatar_url() (previously declared in /home/www/diversitybox.com/wp-includes/link-template.php:3414) in /home/www/diversitybox.com/wp-content/themes/allegro-theme/functions/filters.php on line 147

Now i’vce tried eberything i saw on forums but to no avail i had to delete the theme VIA FTP then install the latest update of the theme still to no avail.Please what do I do and how do i go about this

ANy HELP!!!!!!