GLPI, as any other PHP application is by default limited to the maximum size of the uploaded file of 2MB.

This is because of the factory PHP settings on most Linux distributions and can be easily modified in your php.ini file. You should change these directives, even though upload_max_filesize is directly relevant only:

upload_max_filesize
post_max_size
memory_limit
max_execution_time

Make sure to use the correct units, php.ini should be located at:

/etc/php.ini

Once you are done, restart Apache using this command:

/etc/init.d/httpd restart

Sidenote

If the upload_max_filesize is larger than post_max_size, you must increase post_max_size so that it is bigger than upload_max_size.

If the value of post_max_size is larger than memory_limit, you must increase memory_limit so that it is larger than post_max_size.