Backup both your database and website ... then follow the instructions that I posted ...

If you used the templates and overrides method, you should find your /new_shop working when you are done ...

If not, you can take your time to get things working ...

Or, if totally lost you can always post in Commercial Help Wanted for someone to help you do the Upgrade ...

As learning upgrades is just a matter of taking your time and learning your site better ... it is worth trying the upgrade in the /new_shop as you can always start over until you have it done perfectly ...