I get similar errors in my error_log in php when users are uploading their files
PHP Warning: POST Content-Length of 11933650 bytes exceeds the limi
If you are using Php 5.6.X versions in windows using Wamp, then file location may be in,
C:\Windows\php.ini
Just try with
post_max_size = 100M;
Try to do changes in Apache one. By that your Wamp/XAMP load .ini file