Upgrading can be quick and easy while not changing a thing on your existing site. Your mileage may vary.

What would be helpful is for us to know whether or not your host has cPanel or some other controller with a file manager, database creation tool, etc. If so, you can use the installation instructions at https://docs.zen-cart.com/user/first...t-using-cpanel to create a new folder called test (instead of catalog or shop) that will contain the new site. You can take your time adding mods and templates you think you will need and leave the old site working.