Can’t Login to wp-admin because of this plugin

Warning: Declaration of Axiom_Plugin_Updater::download_package($package) should be compatible with WP_Upgrader::download_package($package, $check_signatures = false, $hook_extra = Array) in /home/customer/www//public_html/columbus/wp-content/plugins/masterslider/admin/includes/classes/class-axiom-plugin-updater.php on line 29

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/customer/www/.com/public_html/columbus/wp-content/plugins/masterslider/admin/includes/classes/class-axiom-plugin-updater.php:29) in /home/customer/www/.com/public_html/columbus/wp-content/plugins/gantry/functions.php on line 182

Warning: Cannot modify header information – headers already sent by (output started at /home/customer/www/.com/public_html/columbus/wp-content/plugins/masterslider/admin/includes/classes/class-axiom-plugin-updater.php:29) in /home/customer/www/semcooutdoor.com/public_html/columbus/wp-includes/pluggable.php on line 1296