Go to Control Panel>User Accounts and change the name. IS there more than one User account?
However if this is the owner account set up during install or OEM setup it will likely not change the name in Explorer until after reinstall for security reasons.
My guess is you somehow jumbled the name when naming your computer and then setting up the owners account during install. Not knowing you'd already done this you must have created the two named Accounts in addition.
I would simply rename the active Jack account to what you want it and delete the other one. As I said earlier you cannot delete the owner's account set up first during install for security reasons, likely the Jack.Jack-Home-PC account also which carried over the PC name you gave it. So I'd rename and keep that one.
That is the issue .. and where I was trying to get to ... the account that is in use ...(mine)
is "jack.jack-home-pc" I want to simply have it as 'jack'
The one that shows as 'Jack' is empty so I can delete that.
How do I rename it ... if I go to Control Panel > user accounts ... it does not even show up there ?
Then I would start over and follow these steps to Clean Install Windows 7, making sure to get the PC name and User accounts differentiated. Something went wrong during install.