There are many ways to fix this issue. You can perform this edit using an SFTP program (like filezilla) or use FileManager from cpanel.
.htaccess file for your site. This is normally located in
/home/yourusername/public_html\websitename and add the below to the bottom of .htaccess
php_value upload_max_filesize 12M
php_value post_max_size 13M
php_value memory_limit 15M
Adjust the limits if required