The amount of pain depends on whether or not you’ve made any customizations to any of the ServiceNow PagerDuty application components (eg business rules, the script includes, etc). If you’ve made a lot of customizations, you’ll need to rationalize the need for those going forward. If you haven’t made any customizations, your upgrade should be pretty straightforward.
If you find a file you’ve customized, you’ll want to export a copy of that and keep it as a backup, then revert that file back to the store OOTB version. This will ensure a smoother upgrade process with minimal skipped items.
Whichever path you take, it’s critical to review the upgrade log and all skipped items, especially the priority 1/2 items. DO NOT JUST IGNORE THEM AND KEEP WHAT YOU HAVE TODAY FROM v4. There are a lot of updates since v4.0 and you’ll need to really review why the items were skipped and rationalize if you need the customizations or changes going forward into v7.5. If you don’t know how to proceed, take the v7.5 version and make adjustments later if needed.
We’re here to help if you need us!