Update problem

Hi guys,

I tried to upgrade wordpress to 4.2.2 but now it have given an fatal error code. Does anyone know how to get this away?

Fatal error: Cannot redeclare get_avatar_url() (previously declared in /home/elfrin1q/public_html/wp-includes/link-template.php:3414) in /home/elfrin1q/public_html/wp-content/themes/zeyn/lib/custom_functions.php on line 623