PhpMyAdmin by default allows you to import only 2 MB file. In many cases this is just way too little.
In order to increase the values you need to alter your php.ini settings. For example put these in your php.ini to import 50 MB files:
post_max_size = 50M
upload_max_filesize = 50M
You can also create a .htaccess file with the above contents in the phpMyAdmin directory:
php_value post_max_size 50M
php_value upload_max_filesize 50M