Upgrade Kentico 7 to 8 and then to 9

You want to copy the Production environment down locally (database and files), then do the upgrade. I usually negotiate couple days or a week window where no changes should be made.

If there are a lot of database changes (say orders) and you can't afford to have a no-change window, still copy database and site locally, do the full upgrade so you have all the files fixed and document any non-code changes that need to occur for the upgrade, then when ready take down the live site, upgrade, copy and paste your already-fixed code, then push back up.

Just make sure that whenever you do a hotfix/major version upgrade, that you LOAD the website before continuing, it has to run code between 7 to 8, then 8 to 8.1, then 8.1 to 8.2 and 8.2 to 9 that only runs when the site loads.

Are you using source control for your code? You should be, and you should be able to merge up after you fix all the code in your dev branch with no issues with production.

As far as database changes, run the scripts in DEV, if everything works fine, get a backup of your PROD and test the scripts there. If everything works there, then when you push to Production, you pull the latest code, and run the scripts to upgrade.

Jason,

As Trevor mentioned you need to run the upgrade process like:

7.x -> 8.0 (run site)
8.0 -> 8.1 (run site)
8.1 -> 8.2 (run site)
8.2 -> 9.0 (run site)
9.0 -> latest hotfix (run site)

I'd not say, it's NOT realistic to upgrade those 6000 lines of code/errors because the upgrade from 7 -> 8 has A LOT OF API CHANGES! I've done upgrades from 7 -> 8 which have had anywhere from 500 - 10,000 lines of errors which needed to be updated/upgraded.

Of the 6000 lines of code or errors, can you tell which ones are custom and which ones are not? If you can tell this (should be able to based on the directory structure provided for each file/error) you can also review that code and see which custom code can be excluded and convert it to use out of the box features, web parts or settings. If all fails, reach out to a partner like myself or any other partner on the Kentico.com website to help you.