This is my first ever upgrade, could someone kindly list the steps necessary to do this orderly.
 
A) Download latest version (v3.5.15)
B) Unzip on my computer
C) Backup files of my Website
D) FTP the new files over to my host site using Binary mode.
E) Go to admin>system upgrade
F) Ensure all my previous modified files (CSS, images etc) are replaced over the new ones.
 
What other steps in between or after have I missed?
 
Seems there is a lot of info but not all in one place. You would think we would have a simple step by step documentation of this and when errors are found they would be added to this documentation on an ongoing basis.
 
Please advise.

Goto admin - System - system upgrade... run the upgrade..

You run the last upgrade after you have transferred over all the software.
 
So are those the steps I follow, or is there anything that I am missing.

Latest version is not 3.5.15 imho?
 
These different version numbers are confusing. What is the latest 3.5 build (afaik 3.5.7) and what's up with 3.6?

You are right it is 3.5.35. How do you edit a message in this forum?

Register and then you will have "Edit" option

I did the upgrade, I have a couple of errs on shipping modules that support is looking into. other then that it went pretty smoothly.
once all is well and running, i can list the steps i took.