1. login as root on your server

2. edit your nginx configuration:
*you can use any text editor that you want. I love nano..

# nano /usr/local/emps/etc/nginx/nginx.conf

3. find http section:

        ############################
        # HTTP Connection - ENDUSER
        ############################

add "client_max_body_size 20M;" under the title.. it will be like this:

        ############################
        # HTTP Connection - ENDUSER
        ############################
client_max_body_size 20M;

4.Save and close the editor.

5. run this commands:

# /usr/sbin/nginx -t
# /usr/sbin/nginx -s reload

6. you are done