The answer was on https://wiki.openwrt.org/doc/howto/secure.access but it looks like you have to use SSH to do this:

in CLI go to /etc/config and edit uhttpd
Code:
....
config uhttpd 'main'
       list listen_http '0.0.0.0:80'
       list listen_https '0.0.0.0:443'
       option home '/www'
       option .....

remove the line that listens to http and the code becomes

Code:
....
config uhttpd 'main'
       list listen_https '0.0.0.0:443'
       option home '/www'
       option .....

this is the same as the CLI commands 


uci delete uhttpd.main.listen_http
uci commit


fuond on the OpenWRT link.

Next step is to restart the http deamon

/etc/init.d/uhttpd restart