Hello,
my name is Josef, i'm experienced Magento developer and administrator, and i would like to offer you my services. I have upgraded various Magento websites before, therefore i know exactly what's need to be done, and how to do it. The simplest way of upgrading Magento is by making staging version of the website including all code and content, and performing the upgrade while the original version is still running. When the website is upgraded and checked for errors, then the two versions are swapped, and the final upgrade of the latest data is performed. To be sure the downtime is minimal, the SSH or at least Control panel with file manager is required to perform the final step of upgrade. I hope you will pick me for this project and i'm looking forward to our cooperation. If you would like to proceed, please contact me first by chat, where we can discuss the details.
Kind regards,
Josef