There are a number of good guides freely available on the internet. I've dropped a couple here:
If you go the basic route it is pretty much follow your nose so is there any particular part you are having trouble with?
Good video for vSphere HA: Enabling Basic Configuration For vCenter (HA) High Availability | vSphere - YouTube
This link shows how to patch a vcha environment, for example from U1 to U2, if you do go to 6.7 however vcha will have to be destroyed and reconfigured. There is pro's and cons's for doing that before patch as well potentially...
Some confusion here - and upgrade would be a jump to a major release, like 6.5 to 6.7 etc, you can use the command line or VAMI on the vcsa to patch it from 6.5u1 to 6.5u2 ( ensuring you have a valid back up )
Then do vcha.