Using installatron to install the latest Joomla is fairly simple. Go ahead and start the process by going to Directadmin/installatron/install/joomla
One of the options is which folder it shoudlbe installed in and it will have prefilled in "joomla" - backspace over that "joomla" to clear it out so that it will install it into the base of your site instead of into the joomla sub folder.
Another important option that can be confusing is the FTP - fill it in with your Directadmin/FTP username and password and for FTP base directory add "/public_html"
Select "continue" to finish the install.
Then once it is installed you need to change the permissions on 2 folders.
Change the "public_html/tmp" and "public_html/cache" folders to "777" permissions. This is needed so Joomla extensions will properly install.
That's about it - remember your Joomla admin login details that you entered during the install process.
Remember to go to www.joomla.org to view and download all the great free add ons - extensions - including great templates to change the look of the site. There are over 3000 extensions.