Getting alot of posts from people just starting out or trying to use versions higher than 7.6 which will cause nothing but headaches. Here is a post of info for people in both categories.

Don't run any version higher than 7.6 as there are numerous bugs and security issues with the later versions. Also never go live with your site until you've applied chatserv's patch for your version. He tirelessly goes through and fixes a ton of issues, drop by and thank him for his work as well.

Download the 7.6 install and install it per the instructions.
Download the 7.6 patch, backup your site and install the patch per the instructions.

Another option is Raven's 7.6 distribution that comes prepatched, with a great installer, and also comes with sentinel for security.

Read more about Raven's 7.6 distro.
Download Raven's 7.6 distro.