MyBB Community Forums

Hello, it's urgent ...
I mistakenly installed my forum on https://forum.slimfirmware.com 
now I want to change the URL to https://slimfirmware.com
I have tried Solution for mybb 1.6, but not working. how can I change it on mybb 1.8?

log into forum admin panel. put forum offline
at the Site Details page, for board url enter https://slimfirmware.com
put .slimfirmware.com as cookie domain [note: it has a dot at the beginning]
enter / (i.e. just a slash) for the cookie path & save the settings

then move all folders & files you have at forum folder to its parent folder (eg. public_html)

close your browser , reopen it & then visit https://slimfirmware.com
if it is working fine then you can put your forum online