https://www.google.co.uk/#q=upload_max_filesize+php
You need to change your PHP settings to allow for larger uploads. PHP has limits on these for a number of things. POST size, upload size etc
Edit: /etc/php5/fpm/php.ini and change these values to something sensible.
NOTE: post_max_size should be larger than upload_max_filesize, this is what I use on normal sites (large forum with uploads).
; Maximum size of POST data that PHP will accept.
; Its value may be 0 to disable the limit. It is ignored if POST data reading
; is disabled through enable_post_data_reading.
; http://php.net/post-max-size
post_max_size = 125M
; Maximum allowed size for uploaded files.
; http://php.net/upload-max-filesize
upload_max_filesize = 100M
; Maximum number of files that can be uploaded via a single request
max_file_uploads = 20