How can I change the filesize limit for imported files in PhpMyAdmin

The filesize limit is not defined in PhpMyAdmin. The limit is taken from php.ini file. To change this limit, you needed to edit your php.ini file:

$ locate php.ini
$ cd /etc/php5/apache2/
$ sudo cp php.ini php.ini.original  
$ sudo vi php.ini

Change the following two variables in the php.ini file:

upload_max_filesize = 50M
post_max_size = 200M

This would allow file uploads of 50 megabytes. You need to restart apache before these changes can take place. On Ubuntu, the command is

$ sudo /etc/init.d/apache2/restart