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