I will upgrade your Opencart store version 1.5.x or 2.x to latest Opencart version. The standard upgrade procedure is described as follows
I will backup your database and existing files just in case.
Store downtime is generally 30 minutes.
I will migrate all store's data to fresh installed Opencart 3.x with no lose (I done that more than 100 times).
I will deliver job with Opencart default theme.
Your current theme won't work on newer version of Opencart.
I will install new theme if you provide me that as compatible with new opencart. (This service requires extra fee)
Your current 3rd party modules will be totaly removed after upgrade. I can install newer version of 3rd party extensions after upgrade. (This service requires extra fee)
All Opencart basic modules will be placed as they are.
I will need admin and cPanel access credentials of your Opencart store.