Sadly at the current time there is no update routine within Softaculous. BUT on your Admin panel you should have a link to the 1.1.9 version and you can easily update versions within Apanel. However, your softaculous will continue to show it as 1.1.8 but if you check your versions within Admin you will see it is 1.1.9
I believe Admins are aware and hope to have the Softaculous updater available in the future.
Here's the info from the docs
http://www.abantecart.com/ecommerce-documentation/56-admin-user-manual/system/updaterALSO - be sure you make a backup of your exisitng within Softaculous BEFORE you run update. I know the updater makes a backup, but it is always good to have more than one place to recover.
You can also clone your existing site using Softaculous - run the update on the clone - test to see all is well. Then run it on your live site.
It is easy - but I prefer to be doubly sure before I mess up a working website.
Lee