By setting it to port 80 the web server is now running on port 80, but tls (https) is still enabled.
To access the sensor you would have to use:
https://:80
If you also want tls to be disabled so everything is in clear text (no encryption) then you would need to execut the following commands:
conf t
service web-server
enable-tls false
exit
And answer "yes" when asked to apply the changes.
Then you can access the sensor with just:
http://